Baker originally was to have an operation to repair the flexor pronator tendon in his right elbow. The Twins said that when New York Mets medical director Dr. David Altchek operated, he determined Baker's ulnar collateral ligament needed to be replaced.
The Twins had said last week that Baker was going to miss the entire season because of the elbow, which has bothered the 30-year-old for more than a year.
Minnesota's 2011 Opening Day starter, he went 8-6 with 3.14 ERA in 21 starts last year. Baker is eligible for free agency after the season.