Sauber endured more frustration in Monaco after Kamui Kobayashi and Pedro de la Rosa were forced to retire from the second European race of the season.

Hydraulic problems forced de la Rosa to retire early on while Kobayashi had climbed as high as fifth as others made their pitstops before a gearbox issue saw him left with no option but to park up.

It meant that the team once again failed to trouble the scorers and technical director James Key admitted it was a weekend that the team wasn't keen to repeat.

"It was frustrating in many ways because our drivers were being held up in the race, and there was more to come from the car," he said. "We felt that a strategic call could help us to overtake some cars ahead. We split the strategies of our cars to take advantage of safety car situations. So we had left our options open for the race, but then we saw on the data that we had a significant increase of hydraulic temperatures on Pedro's car.

"Pedro reported that the steering had become particularly heavy. We pitted him and wanted to see what the problem was, but there was clearly a hydraulic pressure problem. We couldn't diagnose it quickly enough to get him back out again into the race. Just a few laps later there was a gearbox issue on Kamui's car. He lost a gear and then couldn't select the next one, which caused him to stop on the track. That problem is currently under investigation.

"We shall learn what we can from this weekend, but look forward to tracks where we think the car will work better and hope for a much more promising showing in Istanbul."