Djokovic and Rune practised for around an hour on an outside court at Flushing Meadows on Friday and were due to train on Arthur Ashe Stadium for the second part to their session.
Rune’s camp told Danish network TV 2 that the hour of practice was played at “a very high level” and revealed they were informed Djokovic “would have to receive treatment to see if he could continue his training.”
The 21-year-old Dane entered Arthur Ashe Stadium and signed autographs for fans as he waited for around half an hour for Djokovic.
Despite his bags being brought to the court and members of his team being present, Djokovic did not arrive for the second part of the session after receiving treatment.
Rune left and continued his training by practising for around an hour on an outside court with a hitting partner made available by the tournament.
The nature of the discomfort that caused Djokovic to stop training for the day is unknown and the tennis great may simply have taken the decision as a precaution as the US Open starts on Monday.
Djokovic partnered tennis icon John McEnroe in an exhibition doubles match against Carlos Alcaraz and Andre Agassi in the Stars of the Open event on Arthur Ashe Stadium earlier this week.
The 37-year-old did not wear a knee brace during the exhibition, but did wear one during practice sessions with Juan Martin del Potro, Alexander Zverev and Rune in New York.
The 24-time Grand Slam champion underwent meniscus surgery in June after tearing the medial meniscus in his right knee during his win against Francisco Cerundolo at the French Open.
