Josh Thomson (Pictures) will undergo surgery on Thursday to repair a damaged shoulder, forcing the American Kickboxing Academy lightweight out of a Showtime-televised Strikeforce title bout against Gilbert Melendez (Pictures), Sherdog.com has learned.

The severity of the shoulder separation, which Thomson aggravated last week while training with "Razor" Rob McCullough (Pictures), is unknown. According to Bob Cook, Thomson's trainer and manager, doctors believe the 29-year-old lightweight would not heal in time to properly train for the once-beaten Melendez.

Thomson, whom Cook said has been bothered by the shoulder for several months, could face a minor scope if doctors don't find significant damage. However, there is a very real possibility that doctors will need to cut into the UFC veteran.

Winning six in a row since a five-round decision loss to Clay Guida (Pictures) nearly two years ago, Thomson (14-2, 1 NC) appeared primed to face Melendez (13-1) in the anticipated 155-pound showdown.