Stan Wawrinka has withdrawn from the Olympics due to a back injury.
The news comes as a major blow to Switzerland's medal chances in Rio as a few weeks back Roger Federer pulled out of the event in order to continue rehabilitation on his knee.
Wawrinka aggravated his back injury in Toronto last week where he reached the semi-finals of the Rogers Cup.
A statement issued by Wawrinka's management company said: "After a medical examination by his doctor in Geneva, the current world number four has to withdraw from the Olympic Games which will start in Rio de Janeiro later this week.
"Stan Wawrinka felt increasing pain during the tournament in Toronto and therefore traveled back to Switzerland in order to consult with his doctor for a complete check-up.
"Following analyses and a MRI scan, local overstress was discovered and he was advised to reduce his physical activity for an undetermined period during which he will undergo further examinations."
Wawrinka himself added: "I am very sad, going to Rio was close to my heart. After Beijing and London, I wanted to live these Games in Brazil.
"Sadly, it's not possible. I wish good luck to all the Swiss athletes who will go to Rio and I will support them from distance."