Michael Schumacher's return to Formula One in Valencia later this month could be scuppered by fitness problems, according to his official spokeswoman.
The seven-time world champion was injured in a motorcycle testing accident earlier this year, and his spokeswoman, Sabine Kehm, admitted that until he had been given the all-clear there was still a possibility that he may not race in the European Grand Prix on 23 August.
"It is not sure yet the neck will hold and the comeback can be started," Kehm said. "It depends on medical investigations. Only after those will it be clear whether he will be able to drive.
"From the very beginning it was made clear Michael would require medical checks. It is normal. Michael is fully geared up, and fully on it. He has been for a week now. But he is a human being, and we have to make sure everything is fine."
Schumacher has already spent a day testing a two-year-old F2007 Ferrari F1 car at Mugello, using GP2 slicks. Following the test, he admitted on his website that his neck hurt following the test.
However, the pain has not curtailed Schumacher's preparations. He claims to have lost 3kg already, and spent yesterday karting with Ferrari test driver Luca Badoer.
"Karting has a very good training effect; that is why today I just jumped into a testing day of the Tony Kart Team in Lonato," Schumacher said on his official website. "There is nothing better for my preparations at the moment; in terms of steering wheel forces, for example, karting is even more difficult than F1.
"And the fact that it has been boiling hot here is simulating the temparatures expected for Valencia. Luca is with me, and together we found again today that karting is just an awful lot of fun."