FORT MYERS, FLA. -- Twins closer Joe Nathan said today that he will undergo Tommy John ligament replacement surgery on his right elbow with an eye toward returning for Opening Day in 2011.

Nathan played catch with pitching coach Rick Anderson this morning. It was Nathan's first throwing session since he suffered a significant tear of his ulnar collateral ligament on March 6.

"Didn't go like we hoped," Nathan said. "We knew it was a long shot, but what this did do is clear my head. Definitely was no gray area. Definitely was on the black side, where it didn't go as well as we like, and we know now we're going to have to go in and get some surgery done, get this thing fixed up."

Nathan said he will have the surgery as soon as possible, though he hasn't decided where or when. The estimated recovery time is 12 months, and Nathan said he's "very confident" he'll be ready for Opening Day next year.

"Any time you're going to be out for the season -- but especially the timing of this, with this ballclub, this new stadium, the excitement -- it's definitely tough," Nathan said. "But right now I've got to take care of myself and get myself ready for next year."

The throwing session took place along the right-field line of Field 5, here at the Lee County Sports Complex. Nathan was making some strong throws before it ended. I couldn't tell from the body language if it had gone good or bad.

Anderson patted Nathan on the back before they walked off the field, expressionless.

"As we kept throwing, it became clear that it was getting harder and harder to play catch," Nathan said. "It became clear that it didn't feel great. This was going to be an easy answer for me to know I wouldn't be able to pitch without getting this thing taken care of."