Former NFL team doctor David Chao speculates via the video that it's a hyperextension.
By video, left knee contact hyperextension injury. Hope he can return with a brace. https://t.co/0C8FxGsIz0— David J. Chao, MD (@ProFootballDoc) November 29, 2015
Houston was running to break up a pass that went by him when Chiefs safety Ron Parker accidentally leg whipped Houston right around the knee area. It looked like there was solid contact as Houston's leg straightened up, almost like it was hyper-extended. The trainers came out to the field and he came out of the game without putting much pressure on his left leg.
The Chiefs are without Dee Ford due to injury so Frank Zombo came into the game to replace Houston, who went to the locker room after the injury.
UPDATE: Seems like good news...
I see Justin Houston walking out of the locker room under his own power with a slight limp. That's a good sign.— Terez A. Paylor (@TerezPaylor) November 29, 2015