The official offering by the Tribune Co. goes first to Major League Baseball, which will conduct a review before delivering it to six groups of potential buyers, The Chicago Tribune reported Wednesday.

Leading the pack of potential owners is a group headed by John Canning, chairman of Madison Dearborn Partners and an 11 percent owner of the rival Milwaukee Brewers.

A Major League source told the Tribune Canning's group has "every leading citizen of Chicago" and a combined net worth of $10 billion to $15 billion.

Five other groups are expected to receive packets including those headed by Omaha's Ricketts family and Dallas Mavericks owner Mark Cuban.

The sale of the Cubs has been delayed for more than a year because Tribune Co. is trying to sell landmark Wrigley Field separately to the Illinois Sports Authority.