Sean Marshall received a spot start against Philadelphia on Sunday, his fifth start of the season. Jason Marquis will start as scheduled Monday, followed by Zambrano and Ryan Dempster against Houston. Rich Harden won't start again until the St. Louis series beginning Sept. 9. Zambrano receives two extra days off, Dempster gets one more day to rest and Harden gets at least 10 more.
"Any time this time of year you can give guys an extra break, it's not a bad thing," pitching coach Larry Rothschild said. "You'd prefer not to have to do it, but you've got to go along with what's happening and adjust to that. We're going to work around that, do the best we can to get guys extra rest."
It's a precautionary measure more than anything. Through Sunday, the Cubs have a 4 1/2-game edge over the Brewers in the National League Central.
"I would hope that what we're doing today puts us in good shape [for September], that's the purpose of it," Rothschild said. "We're looking at this over the long haul for the rest of the season. What's the best way for us to have an opportunity to win the most games? This does it."
The rotation shuffle was made Saturday night, and Rothschild said Zambrano "was a big part of the decision." The Venezuelan ace, who is 13-5 overall, went 1-1 with a 7.43 ERA in five August starts. He gave up six runs and eight hits in 4 1/3 innings Tuesday against Pittsburgh.
The Cubs took measures since that outing to rest his arm. Zambrano, who had a stint on the disabled list with shoulder soreness in June, threw off a mound in front of Rothschild and trainer Mark O'Neal before Sunday's game, but did not talk to the media.
"He's not in any pain at all, his arm feels good," Rothschild said. "He's gone through this ['dead arm' period] every year for the last four or five years. We're at a point in time where his arm feels a little bit heavy, tired. I think everybody goes through that. ... I think as he sees everything coming back, he'll feel better and he'll get back on his stride."
Marshall (3-4) has a 4.03 ERA in 28 appearances. He held Florida to two runs and four hits in five innings and struck out eight in his last start Aug. 16. The left-hander has proven valuable as a fill-in starter.
Manager Lou Piniella said after Dempster's last start that he wanted to shorten up the converted closer for his outing this week. Getting Harden more rest is also a priority.
"We knew coming in that [Harden] is a guy who hasn't pitched much in the last couple years, and we were going to have to watch him," Rothschild said. "You could see his velocity was down a little bit the other day. He needs some extra days right now. This way, we can really back him off and get him a good rest ... hopefully to get him ready to pitch the rest of the season."
Nick Zaccardi is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.