Zack Martin suffered what looked like a serious knee injury in the second quarter of Saturday's preseason game.

Martin, who will undergo an MRI on Sunday, was hurt on a 7-yard run by Rod Smith, on which it appeared that the helmet of a Cincinnati defender hit Martin's knee. Martin limped off the field and spent a good portion of time in the medical tent before heading to the locker room.

"I think the initial evaluation on it was positive, but we'll certainly get that reconfirmed tomorrow," Jason Garrett said.

Martin signed a six-year extension in the offseason with $40 million in guaranteed money as he has emerged as one of the NFL's best guards.