Zambrano has been suspended by the team without pay for the past three games, after he threw a tirade in the dugout Friday that led to a verbal confrontation with teammate Derrek Lee.
"Beginning Wednesday, Carlos will undergo a treatment program with mutually agreed upon doctors from the Players' Association and Major League Baseball," Cubs general manager Jim Hendry said Monday. "Basically, he will have to follow the treatment for his issues and be evaluated properly, and if the program is acted on properly in accordance to what the doctors they signify he needs to work on and improve on, and follow their directives, Carlos will not be reinstated any time until after the All-Star break."
Asked specifically what type of doctor Zambrano would see, Hendry declined to elaborate.
"We've obviously had a lot of transgressions with Carlos in the past so I think we all agreed that it was time to go and get help, then address the apologies later," Hendry said. "It's an unfortunate situation. His actions were certainly inappropriate and as I said on Friday, those actions toward his teammates and staff will not be tolerated. That's why we tried to work to a conclusion as efficiently and as quickly as we could."
Hendry said Zambrano and his agent have not asked for the right-hander to be traded or released. Zambrano is in the middle of a $91.5 million, five-year contract extension he signed in August 2007.
The 29-year-old Zambrano, a three-time All-Star, was a starter nearly his entire major league career before he struggled early this season and the Cubs put him in the bullpen. He later returned to the rotation and is 3-6 with a 5.66 ERA in 22 games this season, including nine starts.
"The doctors will evaluate him in their level of expertise. I am certainly not anywhere close in that level of expertise," Hendry said. "He will be evaluated, then directed on areas to address some of his deficiencies and he will be required by MLB and the Players' Association to follow the directions of the doctor."
Hendry said he spoke with Zambrano before Monday night's game against Pittsburgh.
"We had a nice conversation and he certainly understands the situation and he and his representative obviously signed off on it," Hendry said.
With Zambrano on the restricted list, the Cubs will call up reliever Jeff Stevens from Triple-A Iowa on Tuesday.