Sergio Perez will sit out the rest of the Canadian grand prix weekend.
The Mexican rookie had hoped he was fully recovered from his heavy qualifying crash and concussion in Monaco two weeks ago and was cleared by FIA doctors on Thursday to drive in Montreal.
Perez, 21, was eleventh quickest in morning practice over 27 laps but after the session told his Sauber team he was not feeling well.
The Ferrari-powered Swiss team has therefore appointed McLaren reserve driver Pedro de la Rosa, the Spanish veteran who drove for the team last year, to race in Perez's place for the remainder of the event at the Circuit Gilles Villeneuve.
Sauber's official reserve driver is Mexican teen Esteban Gutierrez, who is understood to not be in Canada this weekend.