Michael Schumacher's spokeswoman Sabine Kehm has indicated that there may be a question of fitness hanging over his return to Formula 1 on 23 August.

"It is not sure yet the neck will hold and the comeback can be started," said Sabine Kehm on Wednesday.

F1 drivers' necks must be strong enough to cope with high G-forces and Schumacher admitted after testing on Tuesday that his "pinches a bit".

He will now undergo routine medical checks to determine if he can return.

Michael Schumacherhas embarked on a rigorous training regime, resulting in him losing over six pounds in weight.

"From the very beginning it was made clear Michael would require medical checks. It is normal," said Kehm.

"It depends on medical investigations. Only after those will it be clear whether he will be able to drive.

"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."