Ralf Schumacher faces a race against time to be fit for next week's French Grand Prix after a heavy crash put him in hospital last night.
Mario Theissen, motorsport director of Williams's engine partners BMW, said that there were doubts about the German driver's presence on the starting grid for the July 4th Magny-Cours race.
"There is clearly a question mark [about his participation]," said Theissen at the U.S Grand Prix. "I cannot tell now what it will be but it has to be his own decision.
"He will stay here overnight in the hospital just as a precaution and tomorrow (Monday) he has to decide what to do."
Schumacher crashed during the US Grand Prix on the fastest part of the course at Indianapolis, spinning on the banking at turn 13 where speeds reach around 320 kph and slamming backwards into the wall before coming to a stop in the middle of the track.
Medical staff spent more than 10 minutes gingerly extricating Schumacher from the shattered car before taking him to hospital for precautionary checks after he had complained of back pains.
"He is in a lot of pain," said team head Frank Williams. "Everything works, his stomach is a bit upset, pretty bruised but he's basically sound. I think he'll probably be there for several days on my interpretation of what I've heard so far."