"It seems pretty inevitable since I'm not pitching the first week," Pettitte said. "I just have to try and get ready. I'm trying to stay away from having any setbacks."
The left-hander left his spring debut on March 7 after one inning with a strained muscle in his throwing elbow.
Although final roster decisions are not expected until this weekend, team officials admit there is a good possibility Pettitte will be placed on the DL.
Pettitte pitched two innings in a minor league game Sunday and will throw again against minor leaguers Thursday or Friday.
"You have to pitch in games ... it's totally different," Pettitte said. "It's a matter of getting my pitch count up. I feel good and I feel healthy."
Pettitte threw 48 pitches during a 14-minute bullpen session on Tuesday.
If placed on the disabled list, Pettitte's stay could be backdated 10 days from opening day, meaning he could be activated as soon as April 10.
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