UFC heavyweight Shane Carwin posted on his official site today that he is pulling out of his January UFC 125 co-main event fight with Roy Nelson.

Carwin had an MRI Monday and may face back surgery that would put him out indefinitely. Even without surgery, he will be out for the next two-to-three months.

From the post:

"In the end my family and manager are right. I owe myself, I owe my fans the best show I can give them. I need to get healthy. I am going to be speaking with the surgeon this week about the surgery. My thoughts are if the surgery fixes it why add 8-12 weeks of physical therapy, epidurals and traction if surgery may still be needed.

The good news is the doctors said I can work on my cardio (they must have seen my last fight lol) with this injury."

Carwin hasn't competed since losing to Brock Lesnar in a heavyweight title unification bout this past July.

This puts the UFC in a bind as the fight was expected to help PPV sales for a main event featuring Lightweight Champion Frankie Edgar vs. Gray Maynard.

Wrestling Observer's Dave Meltzer wrote that the two most viable options for a replacement are Brendan Schaub, who is fresh off his decision win over Gabriel Gonzaga at UFC 121, or Frank Mir.

While a Mir/Nelson fight has been discussed previously, the thought has been that Mir will take on Lesnar for a third time—a fight that would be a major money draw on PPV.