Coach Gary Kubiak said officials were still trying to determine the severity of the injury, but that Schaub was on crutches Monday.
Schaub injured his medial collateral ligament when he was hit in the knee by Jared Allen in the second quarter of Houston's loss to Minnesota on Sunday. He was limping after the hit, but finished the second quarter before being replaced by Sage Rosenfels after halftime.
"He took a heck of a shot and he tried to play through it," Kubiak said. "He was very courageous through the first half, but it was obvious that he couldn't protect himself."
Kubiak said he wasn't sure if Schaub would need surgery and the current treatment plan is for him to rest and stay off his left knee. When he returns he will have to wear a brace.
Schaub has 1,762 yards passing with 10 touchdowns and eight interceptions in seven games this season. He sat out one game earlier this season after spending the night in the hospital with a virus.
Schaub had a tough start to the season, but had improved in the past few weeks to lead the Texans to three straight wins.
"It's very frustrating," Kubiak said. "I know it is for him. He's worked extremely hard to lead this football team and was playing as good as anybody I've been around in the last few weeks ... it's just sad because he was making a ton of progress."
Rosenfels was 4-1 as a starter last season when Schaub was out with various injuries. Things didn't go so well in his only start this season, when his two fumbles allowed the Colts to erase a 17-point fourth-quarter deficit and earn a 31-27 win.
The career backup's teammates remain confident in him despite that performance.
"We haven't lost faith at all," receiver Kevin Walter said. "He played a great game against Indy, except the last three minutes we didn't execute and we turned the ball over. He played a great game and we know he's capable of playing great games. We're going to rally around him."
Rosenfels was better Sunday and threw for both of Houston's offensive scores. He still had his struggles, throwing an interception in the end zone in the third quarter and taking two sacks on Houston's last drive.
He knows he'll be in for a challenge this week against Baltimore.
"This defense isn't going to give you any easy ones so I've got to go out there and play basically perfect football," Rosenfels said. "I can't turn the ball over and I've got to hit guys when they're open and when nothing's open I've got to throw it away and move on because mistakes have been killing us."