Whittaker named undisputed UFC champ

Robert Whittaker has become Australia's first undisputed UFC champion after it emerged Georges St-Pierre had opted out of the middleweight division.

Whittaker will defend the belt for the first time against the former champion Luke Rockhold in the main event at UFC 221 in Perth on February 11.

The Canadian St-Pierre won the belt from Michael Bisping in November, four months after Whittaker defeated Yoel Romero for the interim title while Bisping was injured.

But he has decided to relinquish the title after being diagnosed with ulcerative colitis, an illness that affects his ability to remain in the 185-pound middleweight class.

"My fight at UFC 217 was one of the greatest nights of my life but I now need to take some time to focus on my health," St-Pierre said in a UFC statement.

"Out of respect to the athletes and the sport, I don’t want to hold up the division. I will be giving up my belt and once I’m healthy I look forward to working with the UFC to determine what’s next in my career."

Rockhold, a 33-year-old American, is considered a step down in class from St-Pierre.

St-Pierre, who had not fought since November 2013 before his win over Bisping, is reportedly targeting a big-money fight with Irish superstar Conor McGregor.

McGregor has not fought in the octagon in over a year after he angled his way into a rich boxing bout with Floyd Mayweather.