Sauber confirmed on Tuesday morning that Pedro de la Rosa is leaving the Swiss team with immediate effect.
The Hinwil based outfit said the Spanish veteran will be replaced for the forthcoming Singapore Grand Prix and beyond by former team driver Nick Heidfeld.
The 33-year-old German's contract will run "until the end of the season", added Sauber in a media statement.
The deal begins on Friday, presumably so Heidfeld can test one more time with Pirelli this week in Spain.
"It was a hard decision for me to make and I want to thank Pedro for his professionalism," said team boss Peter Sauber.
"By signing Nick we have a driver we know extremely well who will help us to further judge the comparative potential of our car."
De la Rosa, who returned to the grid this year after seven years as McLaren's test driver, said he was "surprised" by the decision.
"But I respect it and would like to wish everyone good luck for the remainder of the season. I still intend to be in Formula One for 2011," he added.
No mention was made of Heidfeld's role with Pirelli, but it is reported he will have to leave the job, with de la Rosa being an ideal successor.