Sergio Perez says he is now back to 100 per cent fitness after Monaco crash

The Mexican suffered concussion in the shunt at the chicane, and although he was fit enough to race from the European Grand Prix onwards, he now believes that he was not quite in peak condition and that he needed time out of the car to recover fully.

"After my accident, it didn't take me a lot of time to get back into racing," said Perez when asked by AUTOSPORT about his condition. "But it took me a while to be back in the car feeling comfortable and being 100 per cent.

"It took me quite a while to get back to my optimum level and I really needed this break for my head to get properly better.

"I'm 100 per cent now and I'm looking forward to the next part of the reason."

Perez cited Force India, which has made up 12 points during the last two races and is now only nine points behind sixth-placed Sauber in the constructors' championship, as the team's main rival during the final eight races of the season.

The Mexican expects that the advantage will ebb and flow between the two outfits, depending on track configuration and weather conditions.

"There are so many tracks on the calendar that some suit us and some suit Force India, who are our main competition now," said Perez.

"The team is working very hard. I was at Hinwil working last week with my engineers and we are in good shape for the second half of the season."

Sauber has brought a low downforce aero package to Belgium, as is normal for every team, but the next major non-track specific upgrade package is not expected until next month's Singapore Grand Prix.