Kansas City Chiefs outside linebacker Justin Houston returned to practice Thursday, but has not been cleared to play, according to the Kansas City Star.
Houston sustained a head/neck injury last Sunday against the Tennessee Titans and was undergoing the NFL's concussion protocol. Coach Andy Reid said Wednesday that Houston's symptoms were gone. He practiced on a limited basis Thursday.
Houston is second in the league with 8 1/2 sacks. If he cannot play Sunday against the visiting Oakland Raiders, Frank Zombo -- who mainly plays special teams -- will likely start.
Zombo, in his fourth year, had a career-high four sacks in 13 games as a rookie in 2010. He played five games in 2011 and seven games last season. He has two tackles this year.