John Carlson paused to consider a question about the number of concussions he has suffered in his football career, but he politely declined to give an answer.

“I’m going to pass on that,” he said.

This is a sensitive and serious subject for Carlson, the Litchfield, Minn., native and Vikings tight end. He has suffered three known concussions in six NFL seasons and, according to various reports, two additional ones during his college career at Notre Dame.

Carlson’s latest concussion occurred two weeks ago at Baltimore when he was slammed face first onto a frozen field. Carlson missed Sunday’s game against Philadelphia after failing to pass the NFL’s concussion protocol last week.

Carlson eventually passed the necessary steps to return and practiced Wednesday, but he didn’t feel well Thursday and was held out of practice. He must pass certain protocol again in order to be cleared to play Sunday at Cincinnati, according to coach Leslie Frazier.

In a post-practice conversation Wednesday, Carlson said he and his wife, Danielle, will discuss his concussion history in depth after the season, and he indicated that retirement might be an option.

“That’s something that my wife and I will consider,” he said. “After every season it’s an evaluation period because of the nature of our business. Players move around, players get cut, coaches get fired, things happen. So in that sense, every year is an evaluation period and this year will be no different. And the concussion part of it will be in that conversation.”

Carlson has suffered three concussions since 2011. He turns 30 in May, and he acknowledged that his family is concerned about his long-term health and quality of life.