Seven-time major champion Carlos Alcaraz says dealing with "intrusive thoughts" over when he would be able to return from his wrist injury was the most challenging part of his long absence.
Spain's Alcaraz, 23, has not played a singles match since mid-April but says he feels "great" as he prepares to make his comeback at the US Open, which begins in New York on Sunday.
Alcaraz, who beat rival Jannik Sinner in last year's final at Flushing Meadows, starts his title defence against powerful Russian Roman Safiullin in a contest which is likely to examine his lack of competitive action.
"Once I started to practice a little bit but didn't know when I'm going to [return], those thoughts were really difficult to deal with," said Alcaraz.
"I didn't know if I was going to be ready for Cincinnati, for the US Open, or [if] I'm going to miss the whole American swing.
"That was really difficult to deal with, but finally here we are. Those intrusive thoughts were the most difficult things to deal with in this process."