Yoshihito Nishioka was forced to pull out of his US Open match against Miomir Kecmanovic after collapsing to the ground in scary scenes in New York.

The Japanese player could be seen receiving treatment from medics after becoming unwell during the fifth set of their match.

While Nishioka lay down on the ground, his opponent Kecmanovic showed his obvious concern by sitting down next to the 28-year-old and checking on his wellbeing.

With the score left at 6-7, 6-2, 7-5. 5-7, 0-1 in Kecmanovic's favour, Nishioka stopped on the court and slumped to the ground in apparent agony.

Medics quickly rushed to his aid and the situation turned serious with every minute that passed as Nishioka laid motionless on the floor.

He was eventually taken away in a wheelchair after being forced to retire from the match, giving Kecmanovic the victory. But the Serbian was more concerned for his opponent, bringing him water as he sat with him while he underwent treatment.

Nishioka later sent a message out on social media apologising for making his fans feel worried and explained why he suddenly felt unable to continue.

"Thank you for all your support. I apologise for worrying you. I was already feeling cramps around the 33rd point of the 4th set, and I was already cramping when I served at 5-4," Nishioka wrote on X.

"In the final [set], my waist started to spasm more than my legs, and I couldn't stand up. Then my legs started to spasm too. Then my shoulder blades, both hips, sides, and thighs started to spasm repeatedly."

Nishioka also raised concerns about the support from the officials after his request for a stretcher fell on deaf ears. Instead, he was taken away in a wheelchair while he was having "convulsions."

"I started having difficulty breathing, but with the support of my team, I was put into a wheelchair [I asked for a stretcher but it didn't come] and carried away while still having convulsions," he explained.

"The convulsions didn't stop for about an hour, but I'm feeling better now. My body parts are hurting a lot, so I'm going to skip the doubles and go back to Japan."

While Nishioka will head home for some rest, Kecmanovic can look forward to a second-round match-up against 18th seed Lorenzo Musetti at Flushing Meadows.