Pettibone, currently with Triple-A Lehigh Valley, appears to be the most likely candidate to start because Sandberg said it's "safe" to rule out fellow right-hander David Buchanan, who made 93 pitches over five innings in a start with the Iron Pigs on Tuesday. Buchanan would be pitching on short rest on Saturday.
Jeff Manship is another option, but Sandberg said he would only expect Manship to be able to pitch three innings. Manship has starting experience, but has shown value as a long man out of the bullpen.
"He's a luxury right now in the bullpen with the two innings, three-inning possibilities," Sandberg said of Manship. "Length guy. He's that guy in our 'pen right now and he did a nice job in Chicago in that role. He was available for a shorter stint [Tuesday] night and he's more of a longer guy for tonight."
Pettibone pitched five innings on Sunday afternoon for Lehigh Valley, allowing three runs on four hits with two strikeouts and one walk. He had a 4.04 ERA in 18 starts with the Phillies last season.
Pettibone is on the 40-man roster, but the Phillies would need to make a roster move to open a spot for him on the active roster.