Aaron Hernandez undergoes shoulder surgery

Aaron Hernandez has undergone shoulder surgery which is likely to keep him out of the New England Patriots' spring training sessions.

It is not known when the tight end injured his shoulder, but it is understood that the operation took place earlier in the off-season.

It is expected that the 23-year-old will recover from the surgery in time for the pre-season.

Hernandez recently said that he wants to be fit for all 16 games of the regular NFL season in 2013.