Hours after CC Sabathia (mildly strained groin) landed on the 15-day disabled list on Wednesday, June 27--while New York was hosting the Cleveland Indians to conclude a three-game set--Pettitte suffered a fractured left ankle when he was struck by Casey Kotchman's sharp grounder.
The Yankees expected the left-hander's ankle to take at least six weeks to heal.
"I'm not going to be able to run for a while," Pettitte said. "I'm able to do all the bike work and stuff like that, and swim.
"The reason why it's healing up is 'cause everything I'm doing is bicycle [work] and just trying to keep as much weight off of it as I can."
Pettitte will undergo an X-ray examination he hopes will reveal a fully-healed ankle after the Yankees' next road trip, which wraps up in Seattle on Wednesday, July 25.
By then, the 40-year-old veteran will have been sidelined for about four weeks.
"It's feeling better and better every day," Pettitte said. "It's getting to the point where I felt better throwing today in the outfield. Just hoping I can continue to progress along with that."