The singer, who broke his neck earlier this month when the Porsche in which he was travelling hit a wall at 70mph, compared his "trauma compression injury" to that of former Superman actor Christopher Reeve, who was paralysed from the neck down after a horse-riding accident in 1995.
Campbell told Hello: "I feel like the luckiest man alive.
"(The nurse said,) 'Three millimetres this way, you no walk; three millimetres that way, you dead.' It was like how you'd talk to a baby, but I knew what she was trying to say."
The 30-year-old, who suffered the injury on a "lads' driving holiday" in Spain, said that the incident was caused by an oil spillage in the middle of the road.
He said: "Because of the haze, we didn't see that there was a diesel spill on the road. Before we could work out what was going on, it was already too late.
"The car careered out of control on a bend, and we smashed into a wall at 70mph. My first recollection is my friend - the driver - asking if I was okay."