Houston Texans outside linebacker Jadeveon Clowney was officially placed on injured reserve Wednesday and the team signed linebacker Jason Ankrah to the active roster.

Clowney, the first overall pick in the 2014 draft, had microfracture knee surgery Monday. General manager Rick Smith said the rehabilitation period will last nine months. A return in early September is a possibility but his availability for the start of the 2015 season is in doubt.

Clowney injured his knee in Week 1 against the Washington Redskins and had knee surgery later that week to repair a torn meniscus. The rookie from South Carolina came back and played in Week 8 at Tennessee, as well as in Weeks 11 and 12 against the Cleveland Browns and Cincinnati Bengals. Last Wednesday, the Texans announced that Clowney was done for the season.

After meeting with orthopedic surgeon Dr. James Andrews last week, Clowney opted to have the microfracture surgery, which was the second operation on his right knee this year.

The previous surgery, performed in September, repaired cartilage and lateral meniscus damage. Clowney had sports hernia surgery in June and he suffered a concussion in August.

Clowney recorded seven tackles in four games. He had three tackles for a loss.

Ankrah, a rookie outside linebacker from Nebraska, was on the practice squad. He signed with the Texans as an undrafted free agent in May and saw action in Week 2 against the Oakland Raiders, making one tackle.

The Texans also signed defensive end Kourtnei Brown to the practice squad.