The person, who spoke Friday on condition of anonymity because the agreement has not been finalized, says the deal does not include an invitation to major league camp for spring training.
Willis, who will turn 31 on Jan. 12, did not appear in a major league game last season. He went 1-5 with a 5.00 ERA in 13 games with Cincinnati in 2011.
Willis was the NL Rookie of the Year when he won 14 games for the Marlins in 2003. He went 22-10 with a 2.63 ERA in 2005, but hasn't come close to replicating those numbers since that big season.