Andy Pettitte is being "overcautious" as he tries to work his way back to the rotation, as the lefty fears that another setback could keep him from pitching again this season.

"I know now that if I have another setback then we got serious problems and my season is probably over," Pettitte said Tuesday. "Now we're probably going to be overcautious and figure out what we can do to make sure I'm back and what do I need to get ready."

Pettitte, who has a fractured left fibula, had a setback in late July on a West Coast road trip, as he experienced swelling and estimated that it cost him about 10 days in his rehab. His doctor told him a few weeks back that his leg had not healed as well as they had hoped at that point. Pettitte said he had an X-ray on Monday and it "looked good."

Yankees manager Joe Girardi said he plans on having Pettitte again this year, although he agreed that one more setback could prevent Pettitte from pitching again. The veteran is 3-3 with a 3.22 ERA spanning nine starts after coming out of retirement.

"I think if you were to have a two or three weeks' setback you'd be in trouble," Girardi said. "We have to make sure he's right."

The 40-year-old will do some long-tossing this week to try and stretch out his arm. As the Yankees spent the past week on the road, Pettitte stayed behind and spent plenty of time in the pool and doing some light tossing. The big step for him will be when he can be cleared to start throwing off a mound.

Pettitte is eligible to come off the disabled list on Aug. 28, and said he would like to try and start throwing off a mound around Sept. 1. He said that would give him roughly two weeks to get ready and make some starts before the Yankees likely begin the playoffs.

"I'm feeling really good. Obviously, my question is tell me when I can get on the mound. They can't tell me that exactly yet and that's all I care about," Pettitte said. "I'm just trying to do what they tell me to do and taking it as easy as I can until I get on the mound. As soon as I can do it, I can have some kind of an idea of when I can be ready."