At just 26, Cleaver's career was over.
His story bears remarkable similarities to that of Shontayne Hape, the dual code international whose stunning recent revelations over the extent of the damage he suffered from repeated concussions lifted the lid on the simmering pot of concussion issues in professional rugby.
New Zealand Rugby's initial response to Hape's claim that players routinely manipulated the results of computerised concussion tests and under-reported symptoms to avoid being stood down was a one line statement from medical director Dr Ian Murphy.
"We are very confident that the processes we have in place in regard to baseline testing and in-season assessment of players safeguard against attempts to disguise concussions."
The implication was clear - it doesn't happen here. Cleaver, who is at pains to point out that the care he received from Taranaki and the Chiefs was outstanding, tells a different story. Sitting in that changing shed in Invercargill, he was the only one who truly knew how unwell he was.
With his career on the line, he wasn't about to tell anybody just how bad he'd been feeling since copping a blow to the head against Wellington a week earlier.
Nor was he about to mention the knee injury he'd faked to get out of playing club rugby because he didn't want Taranaki to discover his concussion symptoms had returned.
"They were already low on props so I thought they would go and spend all their money buying in some star prop if they thought I was going to be out," he said.
It was the same fear - losing his shot at his dream - that drove Cleaver to play on with concussion symptoms throughout his career.
In one season for Taranaki he suffered three major head knocks. Each time he was sidelined until he could pass a computerised concussion test, but he routinely beat the test long before his symptoms passed.
"Even through my worst head injuries I have normally been able to pass that test. Sometimes I'd fail it for a week or so. But then I'd pass it and I'd still be messed up. I used to get really run down. I'd get so low on energy and dizzy. I'd get sick a lot, catch viruses. I was just wrecked, dragging me feet through this fog."
He played well enough for Taranaki to get picked up by the Chiefs, but by then his concussion issues were becoming insurmountable.
A heavy knock in training before a match against the Crusaders sent him spiralling into that same dark place he would revisit in Invercargill.
"The week before we'd had all of these prop injuries. I wasn't even in line for selection then all of a sudden I had a chance. I thought 'get through the game, do what you have got to do and you'll be right'. Then you've got another week's rest until you have to do it all over again."
The game proved to be his last for the Chiefs. He played as badly as he felt and "came clean".
The Chiefs' medics referred Cleaver to Auckland-based neuropsychologist James Cunningham.
"It went really poorly," says Cleaver. "The results were terrible. That was start of the end, I guess."
Cleaver allowed the Weekend Herald access to his medical file. His cognitive test results are published with this story. His symptoms included sleep disturbance, headaches, fatigue, lowered motivation, irritability, poor tolerance of noise and light, nausea, dizziness and altered smell. The last one was of particular concern.
"That's not so common," says Cunningham. "That's frontal lobe. It's not good."
Cunningham declared Cleaver unfit to play. He was out of action for a year before his symptoms cleared and his cognitive ability returned to acceptable levels. After such a long lay off he felt great. But two weeks before Taranaki assembled for their ITM Cup campaign, Cleaver copped a whack to the head playing for his club Southern. The fog returned. He pretended the problem lay with his knee.
He made the Taranaki squad but didn't last long until suffering another debilitating head knock.
"I was back like I was. I told the doctor and I was stood down."
After five weeks he could pass the computerised cognitive test and his symptoms had improved.
"To be fair I was never right but I wanted it so bad. The first couple of weeks things went quite well. I was never quite right. I always struggled scrummaging, I was getting dizzy and feeling sick."
By now it didn't take much of a knock to leave him floundering. A tap on the head against Wellington sickened him.
"Again I didn't say much. I didn't say anything. We did a heavy scrummaging session a couple of days before we went down to Southland. After that session I was a mess. Sitting on the plane I kept checking the vomit bag in front of me. I didn't have any air sickness or anything. I was just so nauseous.
"When we got down to Southland, I struggled to get out of bed."
It was Cleaver's job to take the forwards through their pre-match drills. Instead, he sat in the changing rooms trying not to throw up. The knockout that came during in the match was almost inevitable.
When he returned to Cunningham his symptoms were the worst the neuropsychologist had ever seen.
"His advice was 'get out'."
A year later, Cleaver is still recovering. He avoids heavy lifting and wears sunglasses even on cloudy days. Life has changed, but he considers himself lucky. He has a job and an income through the family farm, where he will work alongside brother-in-law Craig Clarke - the former Chiefs captain recently forced to retire after also suffering ongoing concussion issues.
Clarke isn't ready to talk publicly about his concussion woes, but he won't need to go far to find someone with a shared experience to chat with.
The property the two will work near Hawera will be a "special-headed farm", jokes Cleaver.
He has nothing but praise for the medical care and support he received during his career.
Rooted in a desire not to let his teammates down, a fear of losing his career and a lack of knowledge, the decisions he made to not declare head knocks and under-report symptoms were down to him.
"It's probably partly that you want to be a bit of a hero and be back playing the next week and not letting the boys down but I didn't understand what concussion was, that it was your brain bouncing around your skull.
"And you know you have got Super contracts in the pipeline. You are hearing things that these guys are looking at you, but sitting on the sideline is not going to get you a contract. Sitting on the sideline is a big issue."
So, when deep down he knew he shouldn't, he played. Until he simply couldn't go on.
"At the end when I got a knock I was useless. I just don't know how I could ever have played on. I was so bad, so dizzy, so sick. Any sort of pushing just wrecked me. I'd lose my balance. I don't know how people continue to function and play any decent sort of footy when they are like that.
"At least with me all of the professional people around me were very aware of it and were all there to help me. I was very lucky in that regard."
The question now, is what price he may ultimately pay.
Research into the long-term effects of sports concussions is equivocal, but Cunningham is convinced suffering multiple head knocks can have a cumulative effect and can lead to degenerative issues later in life.
"From my experience it takes less of a knock to give more deterioration. In my experience that is true. I can't think of an example where it is not.
"The risk of longer-term difficulties increases with each impact.
"You're a few trees short of a forest and when you get older and the trees are naturally falling out, how many have you got left?"
Among players the penny is starting to drop, says Cunningham.
"The young ones are now asking 'should I keep playing'? In the past it was 'pass me to get back'. Now it is 'what is going to happen tomorrow'?"
Awareness first step in tackling concussion threat
Shane Cleaver's story doesn't come from the bad old days, when concussion was a myth and playing on after regaining consciousness from a knock-out blow par for the course.
Cleaver played last season -- 2013. He was carefully monitored, and received expert medical attention and advice throughout his all too brief first-class career.
Shane Cleaver's story suggests systems designed to protect players can be easily sidestepped. Photo / Getty Images
When the Herald published former dual code international Shontayne Hape's harrowing story in May, New Zealand Rugby's view was that the former Kiwis and England star's experiences of playing on through multiple concussions -- and the consequences to his health that came with it -- happened either in another code or another country.
Cleaver's story suggests that isn't the case.
New Zealand Rugby is trying mightily to stop players risking harm or even death by taking the field with post-concussion symptoms. At the professional level, the time allowed for team doctors to administer a pitch-side suspected concussion assessment (PSCA) has been doubled from five to 10 minutes; more robust computerised cognitive testing has been introduced; awareness programmes launched; and strict protocols governing returning to play introduced.
A recent International Rugby Board survey found the number of professional players who reported taking the field while concussed had dropped from 56 per cent to 13 per cent. While that dramatic decline was encouraging, the risks associated with what is known as a second impact meant the figure was still far too high, NZR medical director Ian Murphy said.
"It is never low enough until it is zero, so you've got to keep refining and assessing," Dr Murphy said.
A key difficulty is diagnosing concussion, which will not typically show up on a brain scan and can cause a wide variety of symptoms.
"If I had some way to scan people for symptoms we'd do it, rest assured. It's the challenge of a condition that doesn't have a clearly defined gold standard test," he said. Without that test, concussion detection and management relies to a large degree on self-reporting. From the weekend warrior who just wants to get back out with his mates, to the pro on the verge of All Blacks selection, the motivation to under-report symptoms is powerful.
Even at the top level, systems designed to protect players can be easily sidestepped.
At lower levels, those systems barely exist.
The key to achieving meaningful change is awareness. In that regard, it's people like Cleaver and Hape who are leading the way.
