Nate Marquardt posted the following on his website:

Chael is a tough wrestler and is coming off a win against Yushin Okami. I thought I would get a title fight or a fight with Henderson, but neither fight was available, so I accepted the fight with Sonnen. Honestly I was upset at first. Why should I be fighting a guy that lost to Demian Maia three fights ago? After I thought about it a while, I changed my mind. Sonnen is a great wrestler with decent striking and I don’t want to wait to fight. Now I am pumped to fight and training has been going great! GSP is in town along with Rashad and all the guys. Let’s do this!

It’s good to see that he is amped up and ready to go. Even if Nate should be a heavy favorite coming in it would be very dangerous to take on Chael if your head isn’t in the fight.

The bout was originally talked about for UFC 110, but it is now set for February 6 at UFC 109.

A major middleweight bout is being planned for UFC 110 in Australia according to SportsNet.ca:

While Nate Marquardt (29-8-2) was awaiting a potentially pending bout with Dan Henderson for UFC 108, it appears he has decided to move on and face Chael Sonnen (24-10-1) instead at UFC 110.

Sources have informed me that the two are awaiting bout agreements and will be added to an already stellar card that the UFC is building for their debut in Sydney, Australia in February.

Sonnen is coming off a dominant win over long time top 10 fighter Yushin Okami at UFC 104.  The win established Chael as a legitimate contender in a 185 pound division littered with the bodies of champion Anderson Silva's victims.  A win over Nate Marquardt would almost certainly put Sonnen in a position to get a shot at the UFC's pound-for-pound king.

Nate Marquardt has seemed to be a different fighter in recent fights, displaying a more aggressive and dynamic striking approach.  His most recent win was over Demian Maia in under thirty seconds.  The fight had positioned Marquardt for either a rematch with Anderson Silva or a title eliminator bout with Dan Henderson.  Contractual issues have Henderson on the shelf and Silva is out of a scheduled bout with Vitor Belfort following elbow surgery.

The middleweight situation is such that Marquardt/Sonnen becomes a true marquee fight in the division.