Manager Lou Piniella says he'll probably return during their series at Colorado. Piniella says the reports on Zambrano "were positive" after he threw two scoreless innings for Iowa against Round Rock on Saturday.
Zambrano relieved starter Thomas Diamond in the seventh inning and earned the hold in Iowa's extra-inning victory. He struck out three batters and allowed one hit. Seventeen of his 29 pitches were strikes. He was also 1-for-1 at the plate.
Saturday night's outing was Zambrano's second with Iowa. On Thursday, he threw 15 pitches in a less-than-impressive scoreless inning.
Zambrano was suspended without pay for three days and later put on the restricted list following a dugout argument with Derrek Lee on June 25. He is expected to pitch out of the bullpen when he returns.
In addition to his suspension and time on the restricted list, Zambrano is believed to have undergone anger management therapy with doctors picked by Major League Baseball and Zambrano's agent.
Zambrano does not have to be moved off the restricted list for a minor league stint, only if he is recalled by the Cubs.
Information from The Associated Press contributed to this report.