Fourth-ranked Stan Wawrinka is withdrawing from the Olympics because of injury, leaving the Rio Games without half of the ATP's top 10.
With his announcement Tuesday, two-time major champion Wawrinka joins Swiss teammate Roger Federer in skipping the Rio de Janeiro Olympics. They won a doubles gold medal together at Beijing in 2008.
Another Swiss tennis player, Belinda Bencic, also pulled out of the Olympics.
A statement issued by Wawrinka's management company says he "felt increasing pain" during the Rogers Cup in Toronto last week and was told by his doctor after an MRI exam to "reduce his physical activity for an undetermined period."
The statement does not say where Wawrinka is injured.
The draw for tennis in Rio is Thursday. Play begins Saturday.