"It's an injury that unfortunately … is going to keep him out for an extended period of time," Capuano said. "Hopefully we'll have a better idea at some time moving forward."
Hamonic was injured during the first period of the Islanders' 4-3 defeat of the Columbus Blue Jackets on Thursday when he collided with Blue Jackets forward Scott Hartnell.
In 72 games this season Hamonic has five goals and 21 points, and averages an Islanders-high 23:49 of ice time per game. Hamonic and Nick Leddy had been the Islanders' top defense pair.
The Islanders have six regular-season games remaining, starting Saturday against the Pittsburgh Penguins (1 p.m. ET; ROOT, MSG+, SN, NHL.TV).
"It's a tough situation for us," Capuano said. "You lose your top guys … you look at Leddy and Hamonic and they were playing against top lines and doing a good job."
The Islanders are the first wild card into the Stanley Cup Playoffs in the Eastern Conference, four points ahead of the Flyers. They also are two points behind the New York Rangers for third place in the Metropolitan Division.
Capuano said it was too soon to say how his defense pairs would look moving forward.
"This is a tough time of year to lose key guys," Capuano said. "(Goalie Jaroslav) Halak, Hamonic, (forward Mikhail) Grabovski. We've got to battle through it. Guys are going to get more minutes and put into situations they're not used to. (Marek) Zidlicky and (Ryan) Pulock are there for us now that we can use it. But losing [Hamonic] is a big loss for our hockey team, no doubt about it."
