Yibing Wu has been forced to retire from his tennis match after collapsing against Yosuke Watanuki in Washington, D.C.

Watanuki advanced to the Round of 32 of the Mubadala Citi DC Open with a walkover after the 23-year-old collapsed. Wu, who had been leading 4-1 in the first set, had to be held up before sitting down on the court, with his whole body going limp in front of a concerned crowd.

It was extremely hot in the Washington area, with the local temperature at the time of playing recorded at 33 degrees Celsius. Fans are hoping that his reaction was purely due to the heat, but Wu had a similar incident at Wimbledon this month which is making fans particularly worried.

Wu collapsed against Frances Tiafoe at Wimbledon according to ESPN, with the Chinese tennis player finding it tough to breathe. Wu was checked over by medics and had a heart rate of 187.

Tiafoe waited 15 minutes to see if the match could continue, and amazingly Wu came back out to finish the contest. Wu ultimately lost in straight sets, but won the crowd for his endurance and courage.

"I mean, no, I had no idea what was going on. I was just, I was like, man, this is wild," Tiafoe said on court when reacting to Wu's situation. "Then he, yeah, he told me that his heart was skipping a beat.

"Having problems with his heart and stuff. Felt like he was collapsing in there. He's like, I'm gonna try and play. Once he said that, I was like, Oh, we're about to have a war. He's going to start coming out and playing loose, which we did.

"I was happy he felt all right and he was able to finish the match and play at a high level. I thought the last two sets were super high level. It was fun. We get along really well. I like Wu a lot. We're going to have many more battles."

But Wu was forced to retire this time, and unsurprisingly as he couldn't even stand up without assistance. The official Twitter account of Tennis TV tweeted: "Unfortunately Wu Yibing has been forced to retire, sending Yosuke Watanuki through, 1-4 RET. Get well soon, Yibing."

Wu is currently ranked No. 90 in the ATP standings, although has been as high as No. 54 during his career. Wu made it to the third round of the US Open last year, but his 2023 entry could be in doubt.