A knee injury has forced Anthony Pettis out of his UFC 163 title shot against featherweight champion Jose Aldo Jr. Popular Chan Sung Jung will take his place at HSBC Arena in Rio de Janeiro on Aug. 3. UFC president Dana White tweeted the news on Friday. Pettis then tweeted about his injury, calling it a small tear in my meniscus. Pettis (16-2), the former WEC lightweight champion, jumped the line at featherweight by texting White after Aldo’s UFC 156 victory over Frankie Edgar and receiving the shot. The knee injury continues a string of bad luck for Pettis, who is the only man with a Zuffa victory over current lightweight champ Ben Henderson. Pettis was expected to get a shot at then-champion Edgar, but had to wait when Edgar went to a draw with Gray Maynard on New Year’s Day 2011, which necessitated a rematch. In the interim, Pettis lost to Clay Guida, which shoved him back in the pecking order. Pettis rebounded with three straight wins, but after getting sick of waiting, issued the challenge to Aldo instead. Jung (13-3), meanwhile, has been a fan favorite since losing a heartbreaking spilt decision to Leonard Garcia in one of the most memorable brawls in MMA history at WEC 48, a bout widely regarded as the 2010 Fight of the Year. Since then, he’s evolved from simply a popular name on the card into a legit title contender, with wins over Garcia, Mark Hominick, and Dustin Poirier in his past three fights, the latter of which was MMAFighting.com’s 2012 Fight of the Year. Shoulder surgery sidelined Jung after the Poirier fight. Aldo (22-1) has won 15 consecutive fights and has held the WEC/UFC title since Nov. 2009.