HOUSTON (AP) -- Houston Texans star running back Arian Foster has a groin injury, coach Bill O'Brien said Wednesday after practice.

The second-year head coach said Foster is still being evaluated, but he would miss time, although how much was unspecified.

Foster was second in the NFL in yards rushing per game (95.8) and sixth in total yards rushing (1,246) in 2014.

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"I feel bad for him personally," O'Brien said. "I think he came into this offseason and he really worked extremely hard. Came back here and ran the conditioning test really, really well. Came back and he was practicing well. But as a football team, it's next man up."

The next man up is most likely second-year back Alfred Blue, who spelled Foster in 2014 and rushed for 528 yards and two touchdowns.

Last year's experience is valuable for Blue.

"I would say it helps a lot," he said. "Just getting in there last year, get your feet wet. Started a couple of games. That definitely helps, knowing I've been through it already."

O'Brien is also impressed with third-year back Jonathan Grimes.

The Texans worked out free agent running backs Pierre Thomas, Ben Malena and Joe McKnight on Wednesday, but had not officially signed anyone. O'Brien said the Texans could sign someone as soon as Wednesday afternoon.

Texans offensive tackle Duane Brown said Foster will be missed in the backfield.

"It's tough," he said. "It's part of the game. My heart feels for him. We'll definitely support him as much as possible. As soon as we get him back, it'll be great. We'll see what happens."

The Texans next travel to Richmond, Virginia for joint practices with the Washington Redskins.