According to a source with knowledge of the situation, Pettitte has been experiencing stiffness in his left arm, though it is unclear whether it is his shoulder or elbow that has been bothering him.
The issue could keep the lefthander from taking the mound on Sunday in Anaheim, which would force the Yankees to find yet another arm to fill a spot in the rotation.
Asked about that possibility, Pettitte told the Daily News that he still planned to pitch on Sunday.
"That hasn't even been discussed," Pettitte said. "Do I feel as good as I'd like to, no. But it's that time of year."
Still, the source said that the Yankees are discussing the issue internally leaving the possibility that Pettitte could be skipped.
Pettitte has been hit hard in each of his last two outings, giving up nine runs in 5 1/3 innings against the Angels on July 31 and five runs in five innings on Tuesday night against the Rangers.