Tampa Bay defenseman Victor Hedman will miss four to six weeks after breaking a finger in the Bolts' 4-2 victory at Vancouver on Saturday.
Hedman will have surgery on the injury on Tuesday.
Hedman entered Saturday's game leading the National Hockey League in points (seven) for a defenseman but left partway through the second period. Hedman was seen holding his right hand as he exited the ice and walked through the tunnel into the locker room.
"You feel for Hedman," Cooper said. "Our team, we've got some depth back there. Injuries happen. You really feel for him. He's come out of the gate so strong. He's poised just to build on the year he had last year. Now, he might be sidelined here for a little bit."
The 23-year-old Hedman had three goals and four assists through the Lightning's first four games. He scored the overtime game winner in the season opener against Florida and had recorded a point in each game until Saturday.
"You come out [this season] and feel like the team's doing some good things, and then you lose a big piece of the puzzle," Cooper said.