McLaren boss Martin Whitmarsh has admitted new team driver Sergio Perez has struggled since replacing Lewis Hamilton.After a poor weekend in China, including a rebuke from Kimi Raikkonen following an on-track run-in, F1 commentator Martin Brundle said he would have signed Nico Hulkenberg for 2013 "ten times before (signing) Perez."'GET YOUR ELBOWS OUT'Whitmarsh backed Perez's defensive driving in China, stating that the 23-year-old rookie should put his "elbows" out and "be robust without being dirty".Whitmarsh said: "I know Sergio is not satisfied with his performance at the weekend, nor should he be."He admitted Jenson Button's "fantastic job" in the sister car has made life difficult for Perez."A lot of credit to Jenson, but we as a team have to step up and support a young driver who has an enormous amount of talent. With these sorts of tyres, which are very fragile, with the balance not quite there, with tricky racing, he did a reasonable job."As a young guy in a big team with lots of expectations you are under a lot more scrutiny, and it's tougher when you've a teammate doing a great job, so there is pressure there," he added.