On Sunday, Montreal head coach Michel Therrien revealed what exactly was ailing the forward.
Therrien told NHL.com after his club's 2-1 loss to the Florida Panthers that Parros sustained his second concussion of the season, and will be evaluated on a daily basis.
Parros was originally sent to the penalty box at 2:01 of the first period after going toe-to-toe with Boulton, but officials quickly came over to take the 33-year-old native of Washington, PA., out of the game as a precautionary measure. He did not return.
The six-foot-five, 225-pound winger has already missed 12 games this season due to a concussion. He went through a scary incident when fighting Toronto Maple Leafs forward Colton Orr on opening night, slamming his head on the ice and getting knocked unconscious.
Parros was an eighth-round pick of the Los Angeles Kings (222nd overall) in 1999. He has spent time with the Kings, Colorado Avalanche, Anaheim Ducks, Florida Panthers and the Canadiens.
In 461 career regular-season games, he has 18 goals, 17 assists and has accumulated 1,049 penalty minutes.