CHICAGO -- Cubs ace Carlos Zambrano threw a bullpen session on Wednesday and remained on track to make a rehab start this weekend.
Zambrano went on the 15-day disabled list on May 4, a day after he strained his left hamstring trying to beat out a bunt. He is scheduled to pitch Sunday in Clearwater, Fla., before starting against San Diego on May 22.
"Carlos had a nice bullpen session," manager Lou Piniella said before Chicago played the San Diego Padres. "He threw the ball well. It was encouraging."
Zambrano told ESPNChicago.com that he will throw 75 to 80 pitches on Sunday. When he does get back, however, he said he will take it easier on the basepaths.
"After that, I'm going to be the same I was. After one month I will be the baseball player I've always been."
Information from The Associated Press was used in this report.