Sergio Perez's participation in the Canadian grand prix in two weeks is in doubt.
The Mexican rookie sat out Monaco on Sunday with concussion and a bruised thigh, after his high speed crash in Monaco qualifying on Saturday.
21-year-old Perez spent Saturday night in hospital and he will wake up again in the local Princess Gate on Monday morning for more tests.
British broadcaster the BBC asked Sauber's chief executive Monisha Kaltenborn if there is any danger Perez might also miss his first visit to Montreal.
She said it is "fairly normal" that Perez is spending a second night in hospital.
As for whether he might have to skip Canada, Kaltenborn added: "It's too early to say that. We are confident but of course it all depends on the FIA doctor's decision."
We are confident but of course it all depends on the FIA doctor's decision
Added team boss Peter Sauber: "I hope we can start in Montreal with our regular driver pairing."
The Swiss team's reserve driver is Perez's fellow Mexican Esteban Gutierrez, the reigning GP3 champion.
"I hope we can get back to normal in Montreal," added Sauber technical director James Key.