LAS VEGAS -- UFC welterweight champion Robbie Lawler's first title defense will be against Rory MacDonald on July 11 in Las Vegas.
UFC president Dana White announced the fight during a news conference on Wednesday. The title fight will serve as the co-main event on a UFC 189 pay-per-view inside the MGM Grand Garden Arena.
A featherweight title fight between Jose Aldo (25-1) and Conor McGregor (17-2) had previously been announced as the headliner to the July 11 event.
MacDonald (18-2) had been scheduled to fight Hector Lombard on April 25 in Montreal, but that fight was canceled last week when it was revealed that Lombard (35-4-1) had failed a fight-night drug test after a win against Josh Burkman on Jan. 3.
Fighting out of Tristar Gym in Montreal, MacDonald will take a three-fight winning streak into the championship bout. He and Lawler (25-10) have fought previously -- in November 2013. Lawler won the three-round fight via split decision.
Lawler lifted the 170-pound title from defending champion Johny Hendricks in a split decision victory on Dec. 6.
ESPN.com ranks Lawler and MacDonald the Nos. 1 and 3 welterweights in the world, respectively.