Theo Epstein, the Cubs' president of baseball operations, was asked during a conference call on Thursday about Volstad being a "choir boy" compared to the mercurial Zambrano.
"That had nothing to do with it," Epstein said. "But we do like Volstad's on-field, off-field makeup. We think he'll continue to mature. ... What he does off the field has nothing to do with this move."
The Cubs decided to deal Zambrano and pay a large portion of the $18 million he's owed in 2012 rather than risk him being a distraction again on the team.
"I should point out, too, that you don't have to be choir boys to be accepted into the Cubs clubhouse," Epstein said. "We're not running a popularity contest in our clubhouse. You just have to be a good teammate who is accountable and somebody who teammates can trust, put the team first, prepare hard, play hard. It's not that difficult."
Epstein scouted Volstad himself prior to the 2005 First-Year Player Draft. A selection out of high school, he made his debut in July of 2008. In 103 games over 3 1/2 seasons with the Marlins, he was 32-39 with a 4.59 ERA.
"He's an experienced young veteran and there aren't many guys who have 100-plus big league starts under their belt before their 25th birthday," Epstein said of Volstad, who turned 25 on Sept. 23.
The right-hander has three above-average pitches, Epstein said, including a sinker -- which should help him at Wrigley Field.
"It's hard to establish yourself as a young pitcher in the big leagues," Epstein said. "Most pitchers Chris' age would've spent more time in the Minor Leagues. We do think there's some upside here."
Volstad is in his first arbitration year and coming off a 5-13 season when he struck out 117 over 165 2/3 innings. Besides being a little more quiet than Zambrano, Volstad also is under team control through 2014.
"I came up young and had some growing pains over the last couple of years, but they've all helped," Volstad said. "I've grown a lot."
Volstad went 0-1 in five starts in September with a 2.32 ERA, posting quality starts in four of his five final outings. That includes back-to-back games against the Nationals and Brewers when he went seven innings and yielded one run in each.
"I'm looking to continue how I finished last year," Volstad said. "There's no reason why I can't do that. I'm feeling good, my body's feeling great, and I'm ready to start pitching."
The key, Volstad said, was that he simplified his delivery and attacked more. Now, he's looking forward to calling Wrigley Field home.
"I love it," Volstad said of the Cubs' home park. "The fan base is outstanding. You know the area and the atmosphere is the best in baseball, and I'm excited for that. A ground-ball pitcher, [with] the infield grass, it's going to be great. I'm really excited to start the year."
Volstad joins newly acquired Travis Wood, Matt Garza, Ryan Dempster and likely Randy Wells in the Cubs' rotation.
This is the third trade by Epstein and general manager Jed Hoyer as they continue their roster makeover. So far, they've acquired Ian Stewart and Casey Weathers from the Rockies in exchange for Tyler Colvin and DJ LeMahieu, and dealt Sean Marshall to the Reds for Wood, Dave Sappelt and Minor Leaguer Ronald Torreyes. Chicago also has signed free agent David DeJesus and bid goodbye to Aramis Ramirez, John Grabow and Koyie Hill.