Holmgren said Grossmann is seeing concussion specialists in Pittsburgh for what he said were "vestibular issues."
Grossmann, who was injured during a practice last month, has not played since March 18. He has four points in 30 games but leads the team with 82 blocked shots and is fourth with 81 hits.
Holmgren also said center Danny Briere, who also sustained a concussion during a practice last month, could return to the lineup Thursday against the Ottawa Senators. Briere, who has five goals and eight assists in 26 games, has been skating for about a week.
Jamie improves every game and every year. I've only been with him for two years, but as a player and as a person it seems like every week he's getting stronger and better, and becoming a better leader and better captain. He wants the team to be so successful that he's making himself better as a player.
— Stars forward Tyler Seguin on teammate Jamie Benn, the '14-15 Art Ross Trophy winner
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