Billionaire blogger Mark Cuban is more serious about buying a major league baseball team than he's been letting on. The tech entrepreneur and Dallas Mavericks owner is set to offer $625 million to buy the Chicago Cubs from Tribune Co., according to a source familiar with the matter. "Mark is desperate to buy the Cubs," says the source. "He wants this so bad."

Cuban hasn't responded to a message from Radar, but when asked about the Cubs in the past, he has admitted to being a potential buyer. "I'm always interested in iconic teams or teams from my hometown, but it's a 'nice to do,' not a 'have to do,'" he told TheStreet.com on February 9.

Despite their reputation as perennial disappointments, the Cubs are one of the most valuable franchises in baseball; last year, Forbes estimated the team's worth at $448 million. (The Yankees topped the ranking at more than $1 billion.) Cuban's offer represents a sizable premium over that valuation.

Tribune, which has owned the Cubs since 1981, has been exploring a sale in recent months. The company has a buyout offer on the table from Chicago real estate billionaire Sam Zell, but is reportedly leaning toward restructuring on its own. Asked about the Cuban offer, a Tribune spokesman said, "We do not confirm, deny, or comment on speculation regarding our business or any of our business units."

UPDATE: Despite plenty of advance notice, notorious e-mail/IM-addict Cuban never did get back to us. But when the Chicago Tribune asked him about our report, he claimed it wasn't true. Our source continues to maintain otherwise. One thing's for sure: A smart guy like Mark knows better than to tip his hand.