Tsitsipas looked fine early in the match aganst Popyrin despite his paly being not the best. The Asutralian eventually took the lead thanks to some aggresive play from the baseline with his forehand doing most of the damage. Suddenly Tsitsipsa approached his opponent to retire from the match to the surprise of many including his opponent.
After the match he simply gave a quick explanation:
"I had to do it, I am trying to be precocious for Turin. I felt pain, I don’t want it to get worse. The problem has gotten bigger in the last few weeks."
He would not disclose what sort of injury it was but he has been dealing with a foot injury since before the US Open. He explained back then that it tends to give him pain occasionally. It seems the injury is getting worse as the Greek felt more pain than usual and with the Finals around the corner he does not want to risk it.