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.