Mercedes car issue hindered Rosberg's pace during the Spanish Grand Prix

The German fell from fifth to seventh late on as his tyres wilted and Kamui Kobayashi's Sauber and Sebastian Vettel's Red Bull overtaken him, with McLaren driver Lewis Hamilton doing likewise.

Mercedes technical chief Bob Bell, who was heading the team this weekend in the absence of the unwell Ross Brawn, said a potential technical problem cost Rosberg downforce and made it even harder for him to look after the Pirellis.

"We didn't have the basic pace we needed this afternoon, and we were hampered further with an issue on Nico's car," Bell said.

"There was a clear loss of downforce measurable on the data, which made it even more difficult for Nico to look after the tyres properly, but whether this was down to damage or another factor is something we will have to investigate this evening."

Rosberg admitted that he had been baffled by his tyre situation during the race - while also praising his long-time employer Williams for its return to the top step of the podium with Pastor Maldonado.

"I had no more rubber left on the tyres and I could just see people going by," said Rosberg. "Fifth place would have been an OK result. It's not that good.

"It's been a strange whole weekend. Fantastic for Williams and for Frank and for Maldonado. All well deserved and it's great. For us, just strange. Tyre management is an issue and the way our car handles the tyres."

Although Rosberg's team-mate Michael Schumacher has been highly critical of the 2012 Pirellis and the style of racing they demand, Rosberg said he had no complaints and was simply confused about how to get the best out of the tyres.

"I'm enjoying it but scratching my head at the same time. It's very strange," he said.