Zambrano, the Cubs' Opening Day starter, is making the switch to open a spot in the rotation for Ted Lilly, who will be activated from the disabled list and start on Saturday, and also help in the eighth inning.
"He'll be ready to go by Saturday," Cubs manager Lou Piniella said Thursday.
The news shocked the other Cubs relievers.
"I don't know what to say," closer Carlos Marmol said. "It's tough for him, I think. It was a surprise. I heard Zambrano was going to be a setup guy and I said, 'Wow.'"
Marmol should benefit the most having Zambrano in the bullpen. The Cubs have been trying to find a solid setup pitcher since the start of the season and were hurt when rookie Esmailin Caridad had to go on the disabled list with a strained forearm. So far, Chicago has been outscored 18-8 in the eighth.
"We need help in the eighth-inning role right now, and that's what we're trying to help ourselves in," Piniella said.
Zambrano said Wednesday that he told Piniella he expects to be back in the rotation when the Cubs are in the playoffs.
"He did mention that," Piniella said. "The playoffs are a long, long, long way away. Let's just get through April right now."
The move was expected to be temporary, but no one on the Cubs will say how long Zambrano will be in the bullpen.
"Let's not put a time frame on it -- let's not do that," Piniella said.
Zambrano will need a little more time to warm up before his relief appearances, and Piniella plans on using him only for one inning or 1 1/3 innings and not stretching him out too far.
"It's a shock," Marmol said of the news. "I never thought Zambrano would be in the bullpen. He'll help the team, that's what he says. I agree with him."
Ryan Dempster, Carlos Silva, Randy Wells and Tom Gorzelanny entered Thursday's game with a combined 2.16 ERA in 11 starts. Zambrano was 1-2 with a 7.45 ERA in his four starts. The bullpen needs reinforcements, having compiled a 1-6 record and 6.14 ERA.
|"He'll help the team, that's what he says. I agree with him."|
|-- Carlos Marmol, on Carlos Zambrano's move to the 'pen|
Was Soriano surprised at the news?
"A little surprised," Soriano said, "but for me, it's not a bad idea. He can come in the seventh or eighth inning and set the table for Marmol. We don't have that guy in the bullpen right now."
"I guess they have a plan," rookie reliever James Russell said. "We'll see what they have working up their sleeve."
As for the backpack, the reliever with the least amount of service time is assigned to tote it to the bullpen. It's loaded with gum, candy, sunflower seeds -- whatever the pitchers need to get them through a game.
Asked if he would be carrying it on Friday, which was when he could make his debut in the 'pen for the first time since 2002, Zambrano laughed and said, "No."
"No chance," Marmol said, smiling.
Russell has the backpack now.
"I'm pretty sure I'm keeping it," Russell said.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.