Sources: Rob Gronkowski surgery set

New England Patriots tight end Rob Gronkowski is scheduled to undergo back surgery on Tuesday in Los Angeles, according to sources.

One source said the time Gronkowski will be out will depend on what else, if anything, doctors find when performing the procedure and how Gronkowski responds to surgery. The generally expected time for recovery is 12 weeks. There is some level of concern within parts of the Patriots organization as to when Gronkowski might return.

The Patriots will be opening training camp in late July and Gronkowski isn't expected to be available at that time. The team's regular-season opener is Sept. 8 on the road against the Bills, giving him an 11-week window from the back surgery to the first game.

The surgery, which is different from the back operation Gronkowski had in 2009 that knocked him out of his final college season at Arizona, will be performed by noted spine specialist Robert Watkins.

Watkins operated this week on New York Giants defensive end Jason Pierre-Paul. He also is scheduled to examine the back of New York Yankees infielder Kevin Youkilis next week.

This will mark Gronkowski's fifth surgery since November after four on his left forearm. He also had surgery on his ankle in February 2012.

Gronkowski's agent, Drew Rosenhaus, told Miami radio station WQAM last month that the back surgery was "preventative-maintenance."