The 39-year-old British driver, who had set the fastest time in the morning practice session, misses today's race, which would have been his debut on an oval, after spinning his Ford Cosworth-powered Lola, slamming backwards into the outside wall and sliding to a stop 150 yards down the track.
He was alert and conscious in the car when safety crews reached the scene, but as a precaution he was strapped to a back board before being removed from the wreckage. His car was badly damaged and had punched a small hole in the 9in-thick concrete wall.
The Formula One world champion, who suffered a broken back during the early stages of his career, was flown by helicopter to Phoenix Good Samaritan Hospital where he had a brain scan was also found to have a badly bruised right shoulder.
Dr Stephan Olvey, IndyCar's director of medical affairs, said that Mansell was not expected to be released until this morning. Olvey added, however, that under IndyCar series rules Mansell could not be cleared medically to drive in today's 200-mile race.
Steve Des Georges, a spokesman for the circuit, said: 'Nigel was unconscious for three to four minutes and then he regained consciousness. He was a bit disorientated and he was complaining of back pains, but all his vital signs were stable.'
Mario Andretti, his Newman- Haas team-mate, said: 'Unfortunately this happens. It can happen to anybody. This kind of circuit does not forgive and that's the problem. You can test its limits and then it catches up with you if you go beyond them. It's something you learn after a while. I'm sure Nigel felt very confident out there.'
Another Newman-Haas spokesman, Hank Ives, said: 'There was a hell of an impact. That is clear from the amount of damage and the time it took to get him out.'
Mansell's wife, Rosanne, was at the circuit and had been sitting with him, chatting in a relaxed manner, only minutes before the second session began.
Mansell, who won his debut IndyCar race at Surfers Paradise in Australia last weekend, had the best time in the first practice session, lapping the one-mile track, which is regarded as one of the world's most dangerous, in 20.760sec at an average speed of 173.414mph.
This was quicker than the official track record of 20.952sec, which was clocked by Michael Andretti in qualifying last year.Reuse content