Pedro de la Rosa will race for the Sauber team in this weekend's Canadian Grand Prix after Sergio Perez was forced to withdraw from the event.
Perez had massive a crash during qualifying in Monaco and was unable to compete in the race.
The Sauber driver, who suffered concussion, was given the green light to race in Canada on Thursday.
However, the Mexican rookie felt sick following the first practice session in Montreal, and Sauber has decided to draft in McLaren's reserve Pedro de la Rosa.
The Spanish driver raced for Sauber last year before he was dumped with five races to go and replaced by Nick Heidfeld, now at Renault.
"Of course I wanted to drive and I had no doubt I was alright," said Perez. "But apparently this is unfortunately not the case. I am deeply disappointed.
"I spoke to the team after the session and told them that I'm not a hundred per cent fit. I only want to drive when I'm a hundred per cent well. I need some more time to recover."
Peter Sauber added: "This development hit us by surprise, because Sergio underwent thorough medical checks, first in the hospital in Monaco, then in a hospital in Zürich, and finally, the FIA doctors gave him the green light this Thursday in Montreal. Nobody could have foreseen that he would feel unwell. Maybe we are being overly cautious, but when it's about the health of our drivers we take zero risks.