Bears coach Matt Nagy: Roquan Smith not playing ‘completely a personal matter’

Bears coach Matt Nagy declined to elaborate about why linebacker Roquan Smith, who has become one of the centerpieces of the Bears’ dominant defense in only his second season, didn’t play Sunday against the Vikings.

Strangely, the Bears added Smith to their participation report an hour and 50 minutes before the game, calling him ‘‘doubtful’’ because of a personal reason. Twenty minutes later, he officially was ruled out for the game.

Smith stood on the Bears’ sideline in a navy sweat suit preferred by inactive players. He left before the media was allowed into the Bears’ locker room afterward.

‘‘I’m going to leave it as, it’s completely a personal matter,’’ Nagy said. ‘‘I’m just going to completely leave it at that.’’

Asked whether Smith’s issue could last beyond the game Sunday, Nagy didn’t budge.

‘‘Again, I’m going to try to just — again, it’s personal,’’ Nagy said. ‘‘And I’m just leaving it at that.’’

Smith never had missed a game as a member of the Bears.

‘‘I don’t know what’s going on,’’ fellow linebacker Danny Trevathan said. ‘‘Nobody knows. We’re just here for him. I’m sure he’ll be all right. He’s a good dude.

‘‘So we’ve just got to be here for him. Guys that are in there, don’t let your level of play fall down. You rise to the occasion; you play better.’’

Nick Kwiatkoski said he didn’t know he’d be replacing Smith until Sunday.

‘‘I’ve been here awhile,’’ he said. ‘‘I’ve seen it happen before. That’s why you come in prepared each week like you’re going to play because you never know what can happen.’’

Cornerback Prince Amukamara didn’t answer when he was asked when he found out Smith was out, but he said the Bears played well without him.

‘‘The only way it changed things is that our starter isn’t out there,’’ he said. ‘‘Other than that, it went like clockwork.’’