"I know that now if I have another setback, we've got serious problems and my season's probably over," Pettitte said. "Now we're probably going to be overcautious about what we can do to make sure I'm back."
Pettitte planned to travel on the Yankees' most recent road trip -- to Detroit and Toronto -- to begin long tossing then, but X-rays taken before the team's departure did not convince doctors that the lefty would be able to put necessary pressure on the ankle, which was fractured by a June 27 comebacker.
Pettitte previously traveled with the Yankees to Seattle and pushed himself too much, which created swelling that stunted the healing process, made it difficult to walk and cost him an estimated 10 days in his rehab.
"You have to watch Andy every step of the way," said manager Joe Girardi. "He thought it was going to heal in two weeks and he was going to be back on the mound in four, but that's just Andy. That's the competitive nature in him, so you have to watch what he does to make sure he doesn't do too much."
Girardi said the Yankees still plan to have Pettitte back this season, though a specific timeline remains uncertain.
Pettitte speculated he would need to be throwing off a mound by Sept. 1 in order to pitch in late September and be ready for the postseason. Girardi said Pettitte will need to prove he can throw 100 pitches in a game to be on the postseason roster.
For now, long tossing is the next step toward stretching out Pettitte's arm, while he continues working in a pool and riding a stationary bicycle. The next step would be jogging.
"My question is: 'When can I get on a mound?'" Pettitte said. "[Doctors] can't tell me exactly that yet, and that's all I care about.
"I'm trying to do what they tell me to do and take it as easy as I can until I can get on a mound. As soon as I can do that, I can have some kind of an idea of when I can be ready."