He had Tommy John surgery just before the end of the season. It used to be the standard recovery time was 12-18 months. Now they say 9-12 months.
If it's 9 months, he could be back in the bullpen by March.
If it's 12-18 months, he could miss most or all of the 2013 season.
http://sportsillustrated.cnn.com/2011/writers/will_carroll/03/09/tommy-john-surgery/index.html