Thurston hopes to be fit for North Queensland's clash against Parramatta in Darwin on June 10, but is taking nothing for granted in his frustrating battle with a torn rotator cuff.
"I went for a scan [yesterday] and that confirmed I won't be fit enough to play," Thurston said. "I did some testing [on Wednesday] and the results didn't come back the way that I wanted. I had a chat to the doc and physio and I did not want to believe it.
"There is no surgery [needed] at this stage, hopefully it's only a couple more weeks [of recovery].
"Obviously I'm devastated. I love everything about the Origin campaign, the build-up, the final training run, the buzz around the city, the town and wherever you are. It's devastating not to be a part of it when that two-minute bell goes.
"I was 100 per cent hopeful of playing. I am relieved that the doc has taken it out of my hands because I was keen on playing."
Asked if he would be fit for Origin II, Thurston said: "Fingers crossed. I'm hoping to be back for the Eels game, but if it's not right then I won't be putting myself or the team at risk."
Thurston backed Milford to shine in his Origin debut alongside Maroons halfback Cooper Cronk.
"I congratulated him first," he said. "He just needs to worry about getting his preparation right and the best thing about this team is you only have to worry about yourself. Prepare the best you can and do the job for the team."