Juan Martin Del Potro out to be a pain in the grass

The Argentine was brought up on clay but won this year's US Open on hard court, making grass the only Slam surface on which he has yet to fully impress.

Del Potro said: "I am determined to do well. Many players have done well at Queen's and then gone on to win at Wimbledon."

The 21-year-old is in London preparing for the Barclays World Tour Finals at the O2, with his first match being against Andy Murray on Sunday.