Grouillard joined the Italian Osella team, taking the seat of Nicola Larini, who in return took Grouillard's seat at Ligier. He was not partnered for 1990 as the financially struggling Osella scaled back their operations, meaning Grouillard had to pre-qualify for the races. He managed to qualify in 8th in Phoenix ahead of Nigel Mansell and Alessandro Nannini which amazed many people in Formula One. During the race, Grouillard was hit by Riccardo Patrese's Williams at the second corner and eventually retired after a second collision with the Swiss driver Gregor Foitek. At Brazil, he retired after another collision involving Michele Alboreto. For Imola the car was upgraded, but that did not help the team as Grouillard retired (not before blocking Mansell in qualifying and ruining the Ferrari's qualifying run, earning the Frenchman a fist wave from Mansell, and not for the last time). He also failed to qualify at Monaco. Two consecutive finishes outside the top 10 at Canada and Mexico were followed up with a poor run in pre-qualifying for France, ending up not qualifying for the race and at Silverstone and Hockenheim, where he also failed to qualify along with another failure to pre-qualify at Hungary. Grouillard finished 16th at Spa with retirements at Monza and Jerez with wheel bearing problems that plagued the Frenchman throughout the year.