World No. 4 Argentine tennis star Juan Martin del Potro has fractured his right kneecap, initial medical tests said.

“It’s a very difficult time… it’s a hard blow that leaves me without any strength mentally. It makes it very difficult for me to get back to recovery. I didn’t expect it,” said Del Potro in a statement.

The Argentine player will continue to rest, as his doctors have instructed on Sunday, until he undergoes new tests that will determine more specifically the extent of the injury, Efe news reported.

In the 10th game of the first set against Coric on October 11, Del Potro fell to the ground and after being attended and having a bandage installed returned to the match intending to continue.

However, he ultimately had to withdraw from the match, which he lost 7-5. He underwent tests on Saturday that determined he had broken his right kneecap.

The South American tennis star had to withdraw from his quarterfinals match against Croatia’s Borna Coric at the Masters 1000 final in Shanghai last Thursday.

Serbia’s Novak Djokovic beat Coric on Sunday in the finals.