Epstein, the Cubs' president of baseball operations, made the comments during a one-hour question and answer session Wednesday, part of WGN Radio's "Cubs Corner."
One of the things the Cubs' new front office wants to do is change the culture, which Epstein said involves players being accountable to the organization, their fans and each other. Zambrano, who left a game early last August, has tested that by his behavior and Epstein has given the right-hander steps to take.
"The Carlos Zambrano of 2011 and years previous can't fit into the culture that we have here," Epstein said. "Change needs to happen, and change will happen. Either he'll change and buy in and fit into this culture -- and I understand there are a lot of skeptics around about that, and I understand that, and frankly, I'm skeptical as well.
"He needs to prove to us that he can change and be part of this culture, or we'll change the personnel and move forward with people who are proud to be Cubs and treat their teammates with respect, treat the fans with respect and can be part of a winning culture in the Cubs' clubhouse."
Epstein was asked about the Cubs' recent trade with the Reds in which they sent Sean Marshall to Cincinnati for starter Travis Wood, outfielder Dave Sappelt and Minor League infielder Ronald Torreyes.
Marshall, one of the best left-handed setup pitchers in the game, is the type of pitcher an organization wants, Epstein said, but he added that Chicago needs to look at the bigger picture. Marshall had one year left of club control. He would become a free agent after the 2012 season and, under the new basic agreement, could leave with the Cubs receiving no compensation.
"With what we're trying to accomplish, which is not just win the World Series in 2012 but build something bigger and more sustainable for the long-term, what's more valuable to us?" Epstein said. "One season worth of Sean Marshall or five seasons worth of a 25-year-old left-handed starting pitcher who can go into our starting rotation ... and two prospects we like a lot."
Epstein did inherit some large, long-term contracts such as Alfonso Soriano's -- the outfielder, who turns 36 on Saturday, is owed $54 million over the next three years. A team has three options on how to handle players with large contracts that appear to be more of a burden than a benefit, Epstein said. A team can be creative and make a deal and eat part of the salary, or a team may decide the best move is to release the player and walk away. The third option is to get to know a player better, understand what makes him tick, and provide an infrastructure in which he can improve.
"There's no one way to handle these things," Epstein said. "I think you need to approach it with an open mind, with hard work and creativity and understand it's a game played by human beings and the ability to bounce back is very real."
Wood gave the Cubs a hometown discount when he returned in 2011, signing a one-year, $1.5 million deal. Epstein said the reliever is "exactly the type of guy we want to build a winning culture here in Chicago." The Cubs are negotiating with Wood's agent about a new contract.
"You have a team that really respects a player, wants him back desperately, and you have a player who loves the city, is a huge part of the community here with his family and his foundation and wants to be back," Epstein said. "If we can't work this out, we're doing something wrong."
LaHair, named the Pacific Coast League Most Valuable Player in 2011 after hitting 38 homers at Triple-A Iowa, is the Cubs' starting first baseman this year.
"I think hitters hit no matter where they are, and this kid has hit," Epstein said. "He's hit everywhere he's ever been. You can't dominate the Triple-A level more than he did this year."
Some players are labeled "4A" hitters if they don't have immediate success in the Majors. Epstein doesn't buy into that.
"It's the right time for an organization like us to give him the opportunity," Epstein said.
Dale Sveum, who Epstein called "authentic and genuine," is also getting an opportunity to manage on the North Side.
"He is who he is," Epstein said. "He knows himself, he never tries to be something that he's not. He's perfectly genuine, never tries to put on facades or airs and show players he's something he's not."
Managers are often categorized as either a players' manager or a disciplinarian. Sveum is both.
"What I like about Dale is he's firmly in both camps," Epstein said. "He holds the players to really high standards. This team will have a lot of discipline on the field, off the field. Players will be accountable to Dale, they'll be accountable to each other. There will be no loafing, no excuse for lack of preparation, lack of aggressiveness, lack of hard work.
"But he's also going to be extremely well liked because he's a down-to-earth guy who doesn't try to be something that he's not."
Epstein said he is still good friends with the Red Sox staff, and admitted to using an office at Fenway Park for a conference call to announce the Marshall trade.
The Cubs and Red Sox have yet to resolve the matter of compensation for Epstein, who left Boston with one year remaining on his contract.
"It's still on the table," Epstein said. "We'll get it resolved. I think both clubs are approaching it in good faith. We need to find a resolution that both parties are happy with."
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter@CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.