The 27-year-old defenseman, who won the Norris Trophy last season, was injured in the second period of a 3-2 win at the Vegas Golden Knights on Friday when he was hit by forward Ryan Reaves. Hedman left the game at 3:08 of the second.
Hedman, who has four points (two goals, two assists) in nine games, will be re-evaluated in a week, the Lightning said.
Defenseman Cameron Gaunce was recalled from Syracuse of the American Hockey League.
Forward Ondrej Palat is day to day after sustaining a lower-body injury blocking a shot in the third period against the Golden Knights.
The Lightning had their seven-game point streak (6-0-1) end in a 7-1 loss to the Arizona Coyotes on Saturday.
