The 37-year-old former England captain joined the French club on transfer deadline day in a deal that will see all of his wages go to a local children's charity.
"He was on holiday but he has already started to train," Ancelotti told reporters. "But he still needs two weeks to be in good physical condition. After, we will see what happens.
"If he deserves to play, he will play. He can play as a defensive midfielder, or right flank. But he needs to have the merit to play."
Ancelotti was speaking after PSG's 4-0 win at Toulouse in Ligue 1 on Friday night.