UPDATE: Worst is confirmed. Clowney will miss up to six weeks with a torn meniscus, according to NFL.com's Ian Rapoport.

Jadeveon Clowney was forced to leave Sunday's game against Washington with a knee injury. It appears that the injury could be serious. According to NFL.com's Albert Breer, Clowney injured his MCL, and could be sidelined through next week or longer. The rookie linebacker will undergo more testing Monday. The Texans aren't ruling out the worst at the moment:

Texans fear No. 1 overall pick Jadeveon Clowney has a meniscus tear that could require arthroscopic surgery, per source. — Adam Schefter (@AdamSchefter) September 7, 2014

Clowney hurt himself when he landed awkwardly after jumping up while rushing Robert Griffin III. He limped off the field and was noticeably upset, though he was able to go to the locker room under his own power.

Clowney had an impressive 9-yard tackle for loss, but was otherwise quiet during the Houston Texans' win. The Texans should be OK on defense if Clowney's injury means they only have to rely on J.J. Watt to provide some power as a pass rusher.

Clowney has had some trouble staying healthy while in a Texans uniform. He was recently cleared after suffering a concussion during training camp.