Sergio Perez says he will make a decision on whether or not he returns to F1 race action in Valencia following Friday practice.
The Mexican was forced to miss the Monaco Grand Prix after an accident in qualifying and then withdrew from the Canadian Grand Prix after feeling unwell following the opening practice session of the weekend.
Perez remains confident of being back behind the wheel for the European Grand Prix but will leave the final decision until he has had chance to drive in Friday practice.
Should the 21-year-old again feel unwell, then Sauber is likely to call on McLaren test driver Pedro de la Rosa to once again step in as his replacement.
“If I feel 100 per cent fine then I will be back in the car,” Perez told the BBC
, “but if I feel dizzy I will not drive. It's important tomorrow to make sure that everything is fine. It is all up to me as it was in Montreal.
"I have done a lot of regeneration training to get back to a good level because after a few days in hospital you lose quite a lot of power, strength and condition.
"I was in the simulator two days ago and I was doing perfectly fine. Of course, everything changes when you're in the car but I'm quite positive than everything will be OK.
"It was really frustrating to miss the races because of health - and also because they were very good races. I'm more motivated than ever."