According to ufc.com:
The Ultimate Fighting Championship’s initial trip to Minnesota on August 9th just got bigger with today’s signing of the UFC Welterweight Title bout between Champion Georges St-Pierre and number one contender Jon Fitch, which will headline the UFC 87 card at Target Center.A couple of us called this main event on Tuesday. Now it's time to guess who will be replacing Coleman to fight Lesnar.
In other action on the UFC 87 card, heavyweight sensation Brock Lesnar returns home for a pivotal bout in his rise up the UFC ranks. Lesnar was originally scheduled to face UFC Hall of Famer Mark Coleman on August 9th, but a knee injury has forced ‘The Hammer’ to withdraw from the show. Lesnar’s opponent will be announced shortly.