Juan Martin del Potro's season is in jeopardy after the Argentine suffered a fracture of his right patella bone in Shanghai this week.
The world number four retired after a set in his round of 16 meeting with Borna Coric at the Shanghai Rolex Masters.
The news leaves his participation at the Nitto ATP Finals in London next month in serious doubt. del Potro secured his place at the season-concluding championships for the first time since 2013 with a win over Karen Khachanov at the China Open last week.
'It's a very difficult moment'
"It's a very difficult moment. I'm very sad," del Potro states. "It's a hard blow which leaves me without strength."
"It's very difficult for me to think about recovery again. I did not expect this to happen."
The 30-year-old lost in the final of the China Open to Nikoloz Basilashvili, but he has enjoyed his most productive season since 2013.
del Potro captured his first Masters 1000 crown at Indian Wells in the spring before reaching the semifinals of the French Open.
He made the last eight at Wimbledon, falling to Rafael Nadal in a five-set epic, before reaching the final in Los Cabos.
Meanwhile, he contested his first Grand Slam final since 2009 at the US Open, exacting revenge on Nadal but coming up short against a formidable Novak Djokovic.
Wretched luck
del Potro has endured miserable injury luck during his career, twice undergoing surgery to repair his wrists.
That saw him plummet down the ATP rankings, although his return in 2016 yielded a silver medal at the Olympic Games in Rio and Argentina's first Davis Cup success.
His 20th ATP title followed in 2017 before reaching a career-high number three in the world earlier this year.
"In the coming days, the doctors will evaluate the recovery process needed to return," the statement concludes.