HOUSTON -- Linebacker Brian Cushing, the Houston Texans' first-round draft pick, won't play in Saturday's preseason opener against the Kansas City Chiefs and also could miss the second preseason game because of a sprained left knee.

Cushing didn't practice Wednesday and instead watched both workouts with a brace on his knee. Texans coach Gary Kubiak said no one is sure when Cushing was injured, but the knee started bothering the rookie Tuesday night, and he was taken for an MRI.

"It's no big deal," Cushing said. "It's a knee sprain. We'll move forward, and I'll keep getting the mental notes and I'll be healthy soon."

Cushing, the 15th overall pick in the April draft, is expected to start at outside linebacker for the Texans. As a four-year starter at USC, he led the nation's second-ranked defense with 10½ tackles for losses last season.

Kubiak said Cushing will wear a brace for two to four days to reduce swelling and that he will begin rehabilitation after that. Cushing probably won't be healthy in time to participate in the Texans' second preseason game against the New Orleans Saints next weekend, but Kubiak doesn't expect him to sit out past that game.

"We feel very, very positive that Brian's going to be ready to go for this season," Kubiak said. "We don't have any doubt right there. Right now, it's just a matter of settling it down and getting going with the rehab process."

The Texans shuffled their healthy outside linebackers Wednesday to deal with Cushing's absence. Kubiak moved Zac Diles from the weak side to take over Cushing's spot on the strong side. That left Kevin Bentley, who has been the backup for DeMeco Ryans in the middle, as the starter on the weak side.

Diles, now in his third NFL season, started the first eight games of 2008 before breaking his left leg in practice.

"We rose to the occasion this morning, and it's about opportunity, as I always tell you," Kubiak said. "Zac makes an unselfish move for the team to go back and go to work at (strong side)."

After making Cushing the starter almost immediately after the draft, Kubiak isn't looking forward to working without him.

"You hate to see him miss the time, but he's going to be there," Kubiak said. "He's just going to miss some time right now. Naturally you want the group to stay together and work together, so we've got some problems from that standpoint, but that's life."