Left-handed starter Tom Gorzelanny has been sent to the bullpen and will pitch in long relief for the Cubs. Zambrano had been pitching from the pen since April 24, after starting the year in the rotation.
Piniella said before Sunday's game that a corresponding bullpen move would have right-hander Andrew Cashner called up from Triple-A Iowa on Monday, but a Cubs spokesman said that while Cashner's callup is imminent, it wouldn't happen Monday and an exact date hadn't been set.
Cashner, the team's No.1 draft pick in 2008 out of Texas Christian University where he pitched in the bullpen as a closer, had been used by the Cubs as a starter until last week, when he was switched to the bullpen. Cashner is 6-1 with a 2.05 ERA for Double-A Tennessee and Iowa.
"The kid Cashner is coming up and he's throwing the ball very well," Piniella said before Sunday's game. "My history here is to get a young man acclimated and comfortable. Get the nervousness out a little bit and then find the right role."
Cashner, a Conroe, Texas, native, is 6-6 and has a fastball that is regularly-timed a 96-97 mph. Cashner's repertoire includes both a two- and four-seam fastball as well as a slider and a changeup.
Piniella still plans to have a balanced bullpen, saying he'll go with three right-handers, three left-handers and then closer Carlos Marmol at the end. Unless someone is traded or goes on the disabled list, that type of setup would project lefty James Russell going to Triple-A when Cashner joins the Cubs.
The rotation in Pittsburgh is set with Randy Wells going on Monday, Ted Lilly on Tuesday and Zambrano on Wednesday. Wells will pitch on two days rest after throwing only 16 pitches in Friday's 7-1 loss to the St. Louis Cardinals. He allowed five runs on hits to the first six batters.
Bruce Levine covers baseball for ESPNChicago.com