Rick Story steps in at UFC 160

Highly touted welterweight Gunnar Nelson suffered a knee injury that has forced him to withdraw from UFC 160.

Sherdog.com reported Nelson's withdrawal Wednesday.

Nelson was scheduled to fight Mike Pyle at the May 25 event in Las Vegas. UFC officials have since announced that former contender Rick Story has agreed to step in for Nelson.

"Really sorry to be out of UFC 160," Nelson said on Twitter. "Will have surgery, heal fast and be ready for action later this summer! Thanks for all the support."

Nelson made his UFC debut in September amid high expectations from many mixed martial arts insiders. He submitted DaMarques Johnson at 3:34 of the first round.

A seasoned Brazilian jiu-jitsu practitioner, Nelson also has demonstrated advanced stand-up skills. In his second appearance under the UFC banner, Nelson defeated Jorge Santiago by unanimous decision.

Nelson is 2-0 in the Octagon and 11-0-1 overall.

Pyle represented Nelson's stiffest test to date. The 37-year-old, who is 24-8-1 as a pro, will enter the cage at UFC 160 on a three-fight win streak.

Story (15-6) is seeking his second victory in a row. During his most recent bout, on March 15 at UFC 158, Story rediscovered his striking power in registering a first-round TKO of Quinn Mulhern. It was his first knockout victory since August 2010.

Heavyweight champion Cain Velasquez will defend his title against Antonio "Bigfoot" Silva in the UFC 160 main event. It will be the second fight between them in a year. Velasquez beat Silva by first-round TKO on May 26 at UFC 146.