"His actions last night are totally intolerable," general manager Jim Hendry said. "In dealing with the hierarchy at MLB today, this was really the most stringent penalty that our club could enforce without a release."
The action means Zambrano is disallowed from any activity with the club for a period of 30 days without pay. During that period, Major League Baseball and the MLB Players Association will discuss his statements from Friday night. Hendry said he expects the Players Association might file a grievance on the severity of the penalty.
By placing the right-hander on the disqualified list and not the restricted list, the Cubs won't suffer a penalty of playing a man down. The club has yet to decide who will be called up to replace Zambrano, but Hendry planned on speaking with assistant GM Randy Bush about the matter later on.
Hendry said he has not spoken with Zambrano and was unaware of his current whereabouts. As far as he knew, Zambrano was on his way back to Chicago. He has, however, had contact with Zambrano's representative, Barry Praver, who maintained that the right-hander was not retiring.
"Obviously, last night his comments were directed toward retirement mode," Hendry said. "[Praver] informed me early this morning that he was not in retirement mode."
Cubs outfielder Marlon Byrd said he briefly spoke with Zambrano, but the conversation was relatively short.
"I need to hear about what he was going through. I just asked to see how he was today," Byrd said. "He said he was doing a lot better today, and that was it. Once you get an explanation then you can come to grips with what you really think about him."
Byrd believed that Zambrano would eventually return and apologize to both the Cubs and his teammates. But whether or not he ever pitches again for Chicago remains to be seen.
"Zambrano is going to come back and apologize," he said. "I'm sure he's going to pitch again. Where? I don't know. What happened yesterday, I don't know. You can't explain it until you talk to him."
Starting pitcher Ryan Dempster was under the impression that Zambrano likely would not pitch again for the club.
"Probably not. That'd be my guess," he said. "He's made his stance pretty clear with what he wanted to do. He's probably got a lot to find out about. He can go do that."
Would Zambrano's teammates welcome him back when his 30 days are up?
"He's been doing a lot of things, not once or twice," outfielder Alfonso Soriano said. "Gotta think a little bit more. He's a big man, but I think that mentally he's weak."
He later added: "It's 50-50. If he comes and changes his attitude, he's more than welcome."
Most of his teammates were unaware of Zambrano's actions when they immediately returned to the clubhouse Friday night. After giving up a career-high five home runs, Zambrano was ejected with one out in the fifth after throwing inside on consecutive pitches to Braves third baseman Chipper Jones.
That's when he returned to the clubhouse, packed up his belongings and told those in the clubhouse he was retiring.
"His actions last night are very detrimental to his teammates," Hendry said. "There's not much worse than running out on your teammates in the middle of a ballgame, unpacking your locker and announcing your retirement. I think that is a tremendous problem."
Hendry referenced other issues that the club has had with Zambrano but didn't recount specific instances. Zambrano referred to the Cubs as a "Triple-A team" and "embarrassing" earlier in the season and was placed on the restricted list for six weeks last year after a dugout blowup with Derrek Lee.
"We've had other instances of obviously not being the teammate that I would aspire him to be," Hendry said. "Certainly not all of that is public. I think you can tell by the sanction that we're trying to enforce that it's not tolerated. It's not right for the other 24 [players]. It's just totally uncalled for."
Added Dempster: "It's not like it's something new. It's been one after another. We've had to deal with it."
Zambrano, who is 9-7 with a 4.82 ERA in 24 starts for the Cubs this season, has one year remaining on his five-year, $91.5 million contract, with a vesting option for 2013.
Chris Cox is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.