The Kansas City Chiefs placed linebacker Justin Houston on the physically unable to perform (PUP) list, multiple sources confirmed Tuesday.

Houston will miss at least the regular season's first six weeks as a result and is scheduled to see specialist Dr. James Andrews in four weeks.

The four-time Pro Bowler underwent surgery in February to repair his ACL, and head coach Andy Reid confirmed he rejoined the team to begin workouts.

"He's the same as he was before - we’re taking it day-to-day,” Reid said Monday to Terez A. Paylor of the Kansas City Star. "When you're around him, he gives you confidence that he’s going to be ready to go this year, but we'll see how it all works out."

Houston led the NFL with 22 sacks in 2014 and is expected to be a vital component of the team's pass rush upon his return.