The Islanders said on Wednesday that the 24-year-old Hillen remained hospitalized following surgery late Tuesday night into the morning. Hillen was injured in the first period of New York's 7-2 home loss on Tuesday and is expected to be discharged from the hospital on Thursday.
It is the second major injury to the Islanders' defense corps that lost veteran Radek Martinek to a season-ending knee injury in November.
"It's really unfortunate for Jack, who was playing so well," Islanders coach Scott Gordon said Wednesday. "If you look at the defensemen we've lost for long stretches this season -- Radek Martinek and now Jack -- it's been the big minute-munchers for us."
Dustin Kohn, who made his NHL debut while filling in during the past week when defenseman Andy Sutton served a two-game league suspension, was recalled from Bridgeport of the AHL on Wednesday and is expected to take Hillen's place in the lineup. The Islanders will begin a four-game road trip Thursday at Carolina.
Hillen was protecting the area in front of goalie Dwayne Roloson during a power play Tuesday night when Ovechkin wound up for a drive in between the blue line and the circles. Hillen appeared to be hit in the chin and mouth and immediately dropped to the ice with 2:31 left in the period.
Blood pooled in front of Hillen as he was tended to by medical staff members. Ovechkin also checked on Hillen, who skated off even though a stretcher was wheeled onto the ice. Hillen remained down on his knees, hunched over, for several minutes before being helped to his feet.
Hillen's teammates and Ovechkin tapped their sticks on the ice in hockey applause fashion as Hillen went down the tunnel.
"I was worried for the young man," Capitals coach Bruce Boudreau said Tuesday. "You could see all of our guys went over to see if he was OK, too -- Alex being the first guy. Everybody on our bench was standing up when he got up, as well as their guys.
"We hate that. When you've got kids playing hockey and you see that, you hope his face is OK."