Johnson was back on the sideline late to watch Houston (3-1) finish off Ben Roethlisberger and the injury-plagued Steelers (2-2). Houston coach Gary Kubiak said Johnson was to undergo tests last night, so his status remained uncertain for the next game, against Oakland.
"Now, if we have to go without him for a period," Kubiak said, "we're going to have to really ask some guys to step up to the plate."
The Steelers may have to do the same without their franchise quarterback.
Roethlisberger was beat up all day, sacked five times behind an offensive line missing two regular starters. The Steelers also lost running back Rashard Mendenhall (right hamstring), linebacker James Harrison (right eye) and defensive end Aaron Smith (foot sprain) during the game.
Roethlisberger played until the end, but he was wearing a protective boot on his left foot afterward. He wouldn't speculate on his availability for this week's game against Tennessee.
"I don't know. I'm still worrying about this game," he said. "It's still too fresh in my mind to worry about next week yet."
Banged up or not, Harrison ripped the Steelers' performance.
"I'm not happy with any of it," Harrison said. "It's a loss. I'm not trying to look for a silver lining in any of it. We played like garbage. Period. We stink right now."
Foster, meanwhile, finally looked healthy after weeks of nursing a left hamstring strain. He broke a 42-yard touchdown run early in the fourth quarter after the Steelers rallied to tie it at 10. Foster finished with 30 carries.
"It was my first game back, really, fully, and I felt 100 percent," Foster said. "It was a nice welcome back and those guys were really welcoming."
Matt Schaub threw a touchdown pass to Owen Daniels in the first half. The Texans led 10-0 at the break, and an ill-timed penalty cost them another touchdown.
On the final snap before the half, Danieal Manning blocked Shaun Suisham's field-goal attempt, and Johnathan Joseph scooped up the loose ball and ran 61 yards to the end zone. But Manning was flagged for an illegal block well behind Joseph, and the score was nullified.
"A lot of times, when those things happen to teams, they can't overcome them," Kubiak said. "That wasn't the case today."