Brosnan's withdrawal is being reported by multiple media outlets, including ESPN.
Owners estimated Manfred had the support of 20 or 21 teams headed into the meetings this week, Werner of about six and Brosnan one: the Cincinnati Reds. A three-quarters majority, 23 of the 30 teams, is required to elect a commissioner.
Selig, who has run baseball since September 1992, plans to retire in January.
Information from The Associated Press was included in this report.