Juan Martin del Potro's week in Shanghai ended in disaster. In the past, it's been his wrist that causes issues, but this time the recent US Open finalist took a tumble and hurt his knee. 

Facing No. 13 seed Borna Coric, Del Potro retired after dropping the first set 7-5, just after taking a medical time out to have his knee taped.

"I made a weird movement with the knee and hit the floor very hard. I felt intense pain," Del Potro told the ATP, adding that he had attempted to keep playing at first but stopped when his knee kept giving him problems. "I didn’t want any more risks," he added. 

Del Potro immediately had tests done on the injury, and the results showed that he experienced a "fracture of his right patella bone" and that "in the coming days, the doctors will evaluate the recovery process needed to return."

He called the diagnosis "a hard blow that leaves [him] without strength."

It's terrible news for the world No. 4, who has qualified for the year-end ATP Finals in London for the first time since 2013. He had plans to play Basel and Paris as well. 

Coric quickly showed that his win was deserved by making a run to the final, where he lost to Novak Djokovic.