The South African added: "I heard bones in my leg being crushed. While I fought for my life, I thought it was a futile attempt against such a large predator.
"The rangers were shooting into the water close to frighten the crocodile.
"I managed to find its head while it was swimming into deeper water for the inevitable drowning. I forced my thumbs into its eye sockets with all my might.
"I think this went on for about five minutes after which I believe the croc was disoriented and literally spat me out close to a sandbank.
"A brave ranger jumped into the river and dragged me to the shore despite the massive risk to himself."
The attack, which occurred in January this year, lasted about 20 minutes and left Mr Knottenbelt with a horrific catalogue of injuries including a broken sternum with bruising of his heart, six broken ribs and a punctured lung.
He also suffered massive tissue damage to his right chest, a dislocated right collarbone, a fractured scapular, broken wrists internal bleeding and multiple severe fractures of the right leg and foot.
Rangers managed to stem Knottenbelt's bleeding with a tourniquet and bits of clothing and he miraculously survived for an hour before a paramedic arrived at the remote location.
He only arrived at the nearest hospital about six hours later. After being stabilised at Mediclinic Polokwane a sedated Knottenbelt was airlifted by helicopter to a Johannesburg hospital. Over the following 14 days he underwent 12 surgeries.
The 71-year-old said: "The infection in my leg and chest was too much for my body to handle.
"Together with a gross infection of my whole body, the massive damage caused to my foot and lower leg necessitated the amputation of my right lower leg through the knee.
"My sons and daughters were prepared for the inevitable but once the amputation had taken place the 'numbers' improved dramatically. I was strong physically and mentally. My recovery started."
After 44 days of in ICU Knottenbelt was transferred to a general ward and then to a rehabilitation centre close to his Benoni home outside Johannesburg.
"I have re-joined the gym and swim an average of 1km daily. I am building strength, of course not as fast as I want, but much faster than anybody including the medical specialists could ever have thought possible.
"I have received a prosthetic leg and I am learning to use it effectively for most situations."
Mr Knottenbelt says he would have definitely died had he not received top class medical care.
The retired 71-year-old said: 'I also believe that many prayers and messages of support have been a driving force in my recovery.
"I thank all those that have supported me over the rescue and recovery period to date.
"I have lived my life positively focused on the development of young people. I still have a lot to offer and this second chance at life stimulates me further to support humanity in any way I can."
