"I don't know the extent of it," head coach John Fox said. "It looked fairly serious."
Quarterback Jay Cutler and right guard Kyle Long both walked over and tried to console Grasu on the sideline before he went back to the locker room. The 2015 third-round pick had enjoyed a solid training camp prior to Saturday's incident.
Fox altered the schedule for the team's annual Family Fest practice last year, holding a 36-play live scrimmage. It was during the scrimmage when Grasu crumpled to the turf as he attempted to block downfield on a screen pass to running back Jacquizz Rodgers.
Grasu started eight games for the Bears as a rookie last season.
Fox, who stopped short of declaring Grasu out for the season, has options at center. Veteran Ted Larsen and 2016 second-round pick Cody Whitehair have worked some at the position in the offseason, and in the early stages of camp.
Larsen has started games before at center in the NFL when he played for the Tampa Bay Buccaneers.
"You guys have seen all the people that have played there," Fox said. "It's not like we have only one. We adjust. That's what you do."