HOUSTON (CBS HOUSTON) — Rookie Texans center Nick Martin just returned to practice earlier this week from a back injury, but he’s already dealing with another health issue.

Martin limped off after the play during Thursday’s joint practice against the New Orleans Saints with apparent lower leg pain. Martin was then carted off the field and did not return to practice.

Head coach Bill O’Brien did not have a prognosis for Martin, though he didn’t believe it will be a serious issue.

“I don’t think it’s serious,” O’Brien said. “It’s not a knee, so I think he’ll be all right.”

Martin is still unlikely to play in the team’s second preseason game on Saturday.

#KHOU11 #Texans rookie center Nick Martin went down as a Saints defender pulled him down. Looks like a twisted knee pic.twitter.com/fyvrvU0Zpr — Matt Musil (@KHOUSportsMatt) August 18, 2016

It’s a major setback for the center, who has been a first-team fixture in camp while earning high praise from O’Brien and his fellow players.

Starting linemen Derek Newton and Duane Brown are also out with injuries and unlikely to be ready until the end of August. The offensive line may not have much time to gel, but O’Brien believes that the developed depth up front could be a silver lining.

“I look at the positive of it, that we’re getting a lot of guys opportunities that will have to play a lot of football for us this year,” O’Brien said. “Whether it’s [Kendall] Lamm or Chris Clark or [Greg] Mancz and [Tony] Bergstrom at center, I think it’s a positive.

“Eventually, we want to have all five who are going to start working together, but we don’t have that right now. So these guys need to keep taking advantage of their opportunities.”

Defensive lineman Christian Covington also exited Thursday’s camp session with an apparent shoulder injury. While he returned to the field, it was sans pads and he did not participate further in practice.

Covington missed nearly a week of Training Camp in the NFL’s concussion protocol, but he did play against the 49ers in Sunday’s preseason opener.