Zambrano was not in the Cubs' bullpen Monday for short duty but will be available Tuesday.
When asked whether the switch meant Zambrano was returning to the rotation, Piniella clarified his statement.
"I didn't say 'rotation,'" Piniella said. "I said we're going to change his role in the bullpen."
The change means the Cubs will rely on lefty Sean Marshall as the prime setup pitcher for Carlos Marmol.
Zambrano talked to Piniella and pitching coach Larry Rothschild about the change before Monday's game.
"[Piniella] told me today there may be a chance to go back to the rotation," Zambrano said. "We'll see how everything works in the next few outings for me."
Zambrano wasn't happy about going from starter to reliever but accepted the switch.
"I'm happy," he said. "As long as this team is happy, I'm happy for this team. Like I said, whatever this team wants me to do, I'll do. This is a business. They're the boss. If the boss wants me to go close games, I'll close games. If the boss wants me to start games, I'll start games. It's their choice."
The Cubs are 11-13 since Zambrano moved to the bullpen, and they have won four of the eight games in which he's pitched in relief. In four starts, he was 1-2 with a 7.45 ERA. On Friday, he was the losing pitcher against the Pirates, giving up three runs on four hits over one inning.
"I had to get used to that role -- it's not that easy," Zambrano said about being the setup man. "The guys out there [in the bullpen], they're used to that. I tried my best, I tried to do my best as setup man. So far, I only had trouble with one game and that was the game against Pittsburgh. I think I did a pretty decent job. I think I did a good job as a setup man."
Zambrano was bumped from the rotation in an attempt to fill a void in the bullpen. The starters -- Ryan Dempster, Ted Lilly, Randy Wells, Carlos Silva and Tom Gorzelanny -- have all pitched well.
"We thought the outcome would be a little different," Piniella said of Zambrano's move. "He's not as comfortable in the bullpen pitching short. We'll use him in a different role and get him some stamina and build up his arm, and that's what we're going to do."
So, the next step is returning to the rotation?
"The next step -- probably down the road [he would go into the rotation] if need be, yes," Piniella said.