José De León needs second Tommy John surgery; updates on Jorge Polanco, Caleb Thielbar

Twins reliever José De León was in positive spirits after he left Saturday's game at Detroit because of an elbow injury, but his worst fears were realized after he underwent a magnetic resonance imaging exam Monday.

De León will require season-ending Tommy John elbow ligament replacement surgery for the second time in his career after he tore his ulnar collateral ligament graft and tore some of his flexor tendon, Twins trainer Nick Paparesta said.

"It's sad because the guys here respect him so much," manager Rocco Baldelli said. "He's suffered through a lot, battled through a lot of different injuries. Nothing has come easy for him ever and he just keeps going."

Other injury updates:

• Second baseman Jorge Polanco, who played only seven games between stints on the injured list because of left hamstring strains, has begun a running progression. "I take full blame for this happening," Paparesta said. "This is my job to make sure these guys are able to get back on the field and not have reoccurring injuries.

"The situation that occurred with him injuring the hamstring again was something we took some time, looked back upon and did a little bit of an evaluation. We had some changes that needed to be made, and that's what we're in the process of doing now. Doing a little bit different type of rehab with him."

• Lefthander Caleb Thielbar is playing catch after he went on the IL because of an oblique strain. He will not return before the All-Star break.