Knee injury sidelines Anthony Pettis

Top-ranked lightweight contender Anthony Pettis suffered a knee injury that has forced him out of an Aug. 3 featherweight title bout with champion Jose Aldo in Rio de Janeiro, UFC president Dana White announced Friday.

"Pettis hurt his knee, Korean Zombie [Chan Sung Jung] will now face Jose Aldo on the Aug card in Rio Brazil," White tweeted.

Pettis, who secured the top lightweight contender ranking in January with a first-round knockout of Donald Cerrone, opted instead to drop to 145 pounds and face Aldo rather than wait for his lightweight title shot against the Benson Henderson-Gilbert Melendez winner. Henderson retained the 155-pound title on April 20 with a split decision.

Competing in a UFC title bout has proved difficult for Pettis since he joined the promotion as the final WEC lightweight champion. He was in line to fight for the title in 2011, but then-titleholder Frankie Edgar and Gray Maynard fought to a draw in January of that year -- and were booked to fight again in October 2011.

A unanimous-decision setback to Clay Guida in June 2011 would knock Pettis from top-contender status. Pettis would win his next three fights to regain the No. 1 lightweight contender spot.

"Injuries are part of the sport, small tear in my meniscus," Pettis said on Twitter. "I was so ready for this fight, this won't stop me. [I will] be back soon."

Jung (13-3) was slated to face Ricardo Lamas on July 6 at UFC 162 in Las Vegas. He has won three fights in a row.

It is not yet known who will fight Lamas next month.