(Carwin in less painful times, leading the crowd in a spirited rendition of "YMCA.")

UFC heavyweight contender Shane Carwin announced today via his website that he will be puling out of his planned UFC 125 bout on January 1 against Roy Nelson to rehab a nagging back injury that could require surgery.

Here’s what Carwin had to say about the situation:

"I am going to pull out of the fight with Roy Nelson. As many of you know I have been having some back pain. I had an MRI yesterday and I have some damage that may really require surgery. If the doctors do not have to perform surgery then I will be out 8-12 weeks. If they do have to perform surgery I do not know how long I will be out of action.

I was really looking forward to fighting again and obviously this is a very disappointing turn of events. My manager said "You can’t fight the best fighters in the world with just heart, it is time to stop limping to the top of the mountain and get healthy so you can climb it on your terms." I have been up all night thinking about this decision and what I may be missing by making it.

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.

This is a hard decision but the right one and I home #TeamCarwin can stand by me through this period of my career. No one wants to get me back to winning more than me. I just need to be healthy to do it.

This type of thing is MMA. I know I am saying that a lot but it is the truth. We sacrifice our minds and bodies on our own time and our own dimes to prepare for battle. in hopes that we get the call for battle. In that process things can go wrong and if we don’t compete we don’t get paid. The time, money and sacrifices are lost and your opportunity might pass you by. Some fighters choose to fight injured as the risk is worth any part of the reward they may receive.

This is why sponsors who support fighters outside of when they fight are critical to this sports success. This is why I am always thanking my sponsors.

If it wasn’t for my sponsors I would not be where I am and I surely would not able to make this very difficult decision right now. Thank you Dethrone, Budlight, Good4UDrinks, and performancemma.com for your continued support. Thank you to my other sponsors and to all of those helping us fighters chase this dream of being a Champion.

Thank you to Jason Genet for being able to make sure that all of my efforts in and out of the ring have value. You and your team have done so much for me and my family words cannot describe how grateful we are.

To my fan’s, we will get there and in the end this is all for you. I hope to continue to entertain you and interact with you as much as possible."

So the question is, who will the UFC get to replace "The Engineer" against "Big Country?"

My money is on Pat Barry or Frank Mir, who would both give Roy a hell of a fight, wherever they it to him.

What will be interesting is whether Carwin will be paired with Brock Lesnar when he returns from his injury since the former champ’s eventual rematch with Cain Velasquez is likely at least eight to 10 months down the road and the UFC won’t want to keep a headliner like Brock on the sidelines that long.

I’m not saying Carwin is angling for an upgrade in opponents, nor am I saying Brock is an upgrade in any other way than he is a higher profile fighter than Nelson, thanks in large part to his WWE popularity and the fact that he was the UFC heavyweight champ, but he may get one simply due to circumstance.