With this Twitter message from UFC president Dana White to his 1.6 million followers, the main event at UFC 137 has now become BJ Penn vs. Nick Diaz. It's being reported that welterweight champion Georges St-Pierre has suffered a knee injury and his fight against Carlos Condit was pulled from the card at UFC 137 in Las Vegas.

"We will sit Carlos to wait for GSP," White wrote. "It's looking so far like he could be ready in a couple months." 

Josh Koscheck has offered to fight Condit on one week's notice, but Condit has decided to wait for GSP to recover.

This is the second time the main event has changed for UFC 137, the first was when Nick Diaz was missing in action and didn't show up for numerous scheduled press events to help promote the card. White made the decision to change St. Pierre opponent from Diaz to Condit for the main event and Diaz later become BJ Penn's opponent.

Injuries to fighters are a problem that plagues mixed martial arts. It’s something that’s unavoidable, but must be improved upon.

A huge case in point is the UFC on Fox bout between heavyweights Cain Velasquez and Junior Dos Santos. I’m sure the UFC is crossing its fingers and toes hoping that no injuries occur during practice. That would be a major blow to the sports if it wants to attract more mainstream fans.

How does the change in the main event affect you buying UFC 137?