World number four Stanislas Wawrinka has withdrawn from the Olympics in Rio de Janeiro due to a back injury.

The 31-year-old was Switzerland's main hope for a medal after Roger Federer pulled out of the Games in order to focus on returning to action next season.

However, the team have been dealt another blow as Wawrinka, who was knocked out of Wimbledon in the second round, is dealing with a back problem.

"I am very sad because after Beijing and London I would have liked to experience my third Olympic Games in Brazil," Wawrinka said in a statement. "Unfortunately that will now not be possible."

The first round of the men's singles tournament will get underway on Saturday.