Pettitte's normal turn would come on Friday, but the Yankees are planning to have Hiroki Kuroda and Phil Hughes pitch the first two games of their series against Seattle. Rainy weather forecasts for this week in New York could also affect the planning.
On Sunday against Triple-A Pawtucket, Pettitte permitted five runs (three earned) on eight hits in five innings, proclaiming himself ready for the Majors after the outing. He threw 92 pitches, walking one and striking out five.
"The reports that I've got have been pretty good," Yankees manager Joe Girardi said. "He struggled a little bit his last start with the command of some of his pitches, but that doesn't mean that he's ready or he's not ready. We feel that he's physically ready, he feels that he's physically ready and that's why he'll be here this weekend."
Cashman also did not witness Pettitte's start in person, but he heard enough from Minor League pitching coordinator Nardi Contreras and others that the Yankees are comfortable advancing Pettitte to the highest level.
"If everybody was telling me no, then I wouldn't do it," Cashman said. "I'm not sure if he'll get anything more by keeping going, to be honest."
The start will be Pettitte's first big league outing since the 2010 American League Championship Series. He came out of retirement this spring after briefly attending camp as a guest instructor, signing a Minor League contract worth $2.5 million on March 16.
New York could use a boost in its rotation, though Pettitte's arrival is likely to impact David Phelps, who has taken over for the ineffective Freddy Garcia as the club's No. 5 starter. Girardi said the club is not prepared to discuss who will leave the rotation.
"We have guys that we want to go out and pitch very well, and we'll make a decision on Sunday who we're going to take out," Girardi said.
The Yankees have expressed confidence that Pettitte will be able to approach the levels of performance he showed in 2010, when he was 11-3 with a 3.28 ERA, but Cashman cautions that his arrival brings no guarantees.
"It would help, but at the same time, there's still the unknown," Cashman said. "If there's a gap between what the old Andy Pettitte is and what we're going to get, I just don't know yet. We're looking forward to adding another healthy arm to the mix here because our depth has been challenged and some of our healthy starters have been inconsistent."
Girardi, for his part, seems to be counting on Pettitte to shake a year's worth of rust off and be at a level close to where he was.
"I think all of us probably kind of expect that we're going to see Andy Pettitte, what we're used to seeing," Girardi said. "A guy that grinds out starts, that has the ability to get double plays, that doesn't panic out there. I think you can only go back on what you've seen from him."
While he waits to be activated, Pettitte cannot work out with the Yankees. Cashman said that Pettitte has a home in Westchester, N.Y., and plans to prepare for his start there. Pettitte told the team that he threw on flat ground on Monday in the New York suburbs, and he also tossed last week in Houston.
"He's a jack of all trades," Cashman said. "He knows exactly what he needs to do to get it done."
Pettitte has pitched 13 of his 16 big league seasons with the Yankees, spending 2004-06 with the Astros, and he ranks as the all-time leader in postseason wins (19), starts (42) and innings pitched (263).
Pettitte's 203 victories as a Yankee rank third in franchise history, behind Hall of Famers Whitey Ford (236) and Red Ruffing (231), and his 1,823 strikeouts are second, only 133 behind Ford's 1,956.
"I think the fans are really excited," Cashman said. "I know Andy is really excited. And I'll be excited obviously if he plugs in and helps us."