The Twins announced on Wednesday that the replacement of May's torn ulnar collateral ligament was successful. The 27-year-old was transitioning back to starting, following a move to the bullpen halfway through the 2015 season.
With May's injury and their release on Tuesday of veteran right-hander Ryan Vogelsong, the Twins are down to Jose Berrios, Tyler Duffey and Adalberto Mejia in the competition for the fifth spot in the rotation.
May was placed on the 60-day disabled list, making room for the Twins to add left-hander Craig Breslow to the 40-man roster. The 36-year-old Breslow is among the finalists for a middle relief role.