HOUSTON -- Arian Foster's rehab is ahead of schedule and will be back "sooner rather than later," Texans coach Bill O'Brien said Monday.

"Arian is doing well," O'Brien said. "Relative to the injury that he has and the prognosis early on, I would say he's ahead of that. But again, like I always say to people, I reserve the right to change my mind. That's how it stands today."

Foster suffered a groin injury in the Texans' first fully padded practice of training camp, which took place on Aug. 3. He had surgery Aug. 7 to repair the injury that involved a muscle being torn from the bone. Sports hernia specialist Dr. William Meyers performed the surgery in Philadelphia.

Significant groin injuries can take three months of recovery time, but Foster's surgery was successful and left reason for optimism.

Foster has been rehabbing in Houston for several weeks.

Arian Foster is ahead of schedule in his recovery from a groin injury, according to coach Bill O'Brien, though there is no immediate timetable for his return to the Texans. Tim Heitman/USA TODAY Sports

"I believe that he's working hard to get back," O'Brien said. "He's a very hard-working guy in that training room. I think he'll be back sooner rather than later relative to what the early prognosis was."

The Texans have three healthy running backs available while Foster remains sidelined: Alfred Blue, Jonathan Grimes and Chris Polk. Blue is likely to start against the Kansas City Chiefs, whom the Texans host in their season opener.