Schaub sustained a Lisfranc injury in Houston's 37-9 win over Tampa Bay on Nov. 13, and had to give up hope on returning this season after meeting with foot specialist Dr. Robert Anderson in Charlotte on Wednesday.
Houston (7-3) placed Schaub on injured reserve, and Leinart will make his first start at Jacksonville (3-7) on Sunday.
Schaub is scheduled to have surgery in Charlotte next Wednesday. Doctors have assured him his injury is not career-threatening and isn't likely to occur again when he returns to action.
"Once I talked to everyone, there really wasn't an option out there, other than to get it fixed for the long term," Schaub said. "It's pretty positive as far as after the surgery, getting the rehab done and being able to come back, play and be fine."
Coach Gary Kubiak said Schaub will travel with the team this weekend and be available to support Leinart, rookie T.J. Yates and third-stringer Kellen Clemens, who signed with Houston on Wednesday.
"He needs to stay very much involved," Kubiak said. "I think there's a way he can help this team, so we're going to give him a chance to do that. It's just tough to see him standing back there."
But Kubiak isn't sure how much Schaub will be able to help after his surgery. Schaub said he faces a long recovery, starting with 6-8 weeks of non-weight-bearing activity.
"It's not a quick turnaround, as far as rehabilitation," Schaub said. "It's going to be an offseason getting ready and getting right for training camp."
Schaub has been the Texans' starter since 2007, after he was acquired in a trade with Atlanta. He missed five games in his first year with the team because of a shoulder injury and concussion, then sat out five more in 2008, one with an illness and four with a knee injury.
Critics questioned his durability, but Schaub silenced them by starting every game between 2009-10 and the first 10 of this season. He hurt his foot in the second quarter against Tampa Bay and played the entire second half, but said he didn't make the injury more severe by staying in that game.
"Talking to the doctors, there wasn't anything I could do worse to it, other than something new," he said.
So far, Houston has survived remarkably well as one key player after another has gone down with an injury, taking control of the AFC South behind the best 10-game start in team history.
Running backs Arian Foster and Ben Tate missed time early, outside linebacker Mario Williams was lost for the season with a torn chest muscle, and star receiver Andre Johnson has sat out six games with a right hamstring injury. Johnson is expected to play in Sunday's game, along with safety Danieal Manning, who broke his left leg in a victory over Tennessee on Oct. 23.
Still, the Texans haven't trailed in four games, hold a two-game lead in the division and seem to be closing in on the team's first playoff appearance.
Schaub says this year's success makes the frustration over this injury more disappointing than the ones he's had in past years.
"The physical side of it and actually getting hurt is part of the game and I can handle that," he said. "Mentally and all that, I can deal with that. I'll be back. I'll get back.
"But after all the hard work I've put in and this team's put in, this organization, to get to this point, with six weeks to go, that's the frustrating part, to not see it through with my team," he said. "That's the frustrating part, to get to this point and not be able to finish it."
Schaub was determined to return to practice on Thursday and be on the sideline Sunday to help Leinart, who will make his first start since 2009, when he played for Arizona. Leinart didn't take a snap last season, and re-signed with the Texans because of his comfort level with Kubiak, Schaub and the Houston system.
Schaub is confident the offense won't miss a beat with Leinart taking the snaps.
"He's been around enough football," Schaub said. "He's played enough, too, it's not too big for him. He's going to go out there, be even-keeled, run the huddle, run the offense and he's going to be in good shape."