However, Zambrano was not expected to join the Cubs during this homestand, which ends next weekend with a series against the St. Louis Cardinals. He most likely will return during the team's next road trip to Houston and Colorado, which begins July 26.
Zambrano was expected to pitch for Iowa either Wednesday or Thursday and also throw in Round Rock when the team travels there for a weekend series.
"He's missed a lot [of time]," Cubs manager Lou Piniella said of Zambrano. "I would think [he'll come back] sometime on the road trip."
Zambrano has been working out since last Thursday in Mesa at the team's facility. He threw about 25 pitches on the side in his first outing. Cubs pitching coach Larry Rothschild and athletic trainer Mark O'Neal are monitoring his program.
Zambrano has not thrown in a game since June 25, when he lasted one inning against the White Sox at U.S. Cellular Field and then threw a tantrum in the dugout, accusing his teammates of not playing behind him. He was suspended for three days and then placed on the restricted list.
When he does return, Zambrano, who was the Cubs' Opening Day starter, will be assigned to the bullpen.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.