Haynesworth hurt his ankle — the Redskins aren't saying which one — in practice Wednesday, the latest setback in an eventful several months for the two-time All-Pro.
"He tested his ankle and wasn't able to go," coach Mike Shanahan said.
Haynesworth played as a backup in the Redskins' victory over the Dallas Cowboys in Week 1, following an offseason and preseason in which he had disputes with Shanahan over the team's defensive scheme, conditioning workouts and playing time.
Also inactive for Washington was safety Kareem Moore, who's been sidelined since the preseason with a sprained right knee.
Texans cornerback Antwaun Molden was out for the second consecutive game with an injured ankle.