Novak Djokovic appeared to be suffering physical issues during the gruelling second set with Daniil Medvedev in the US Open final.
Following one particularly gruelling point at 3-3 in that second set, Djokovic collapsed in a heap on the court.
He was lying on his back looking up at the roof of Arthur Ashe Stadium and was seemingly struggling to catch his breath.
Martina Navratilova, who is commentating for Sky Sports, said: “Another monster rally from Medvedev. Djokovic just collapses.”
Earlier in that same game, the 36-year-old bizarrely stumbled forward after missing a shot.
Djokovic seemed to be struggling throughout the second set and was holding on at points against his Russian opponent.
Medvedev had set points to draw level with the 23-time Grand Slam winner, but failed to convert.
The Serbian superstar eventually claimed that set in a tiebreak after more than 100 minutes of exhausting tennis.
Djokovic had won the first set 6-3 having immediately broken the Medvedev serve.
He is looking to win his 24th Grand Slam title, a fourth in New York, that would see him equal Margaret Court’s all-time record.