Islanders rookie goalie Kevin Poulin will miss the rest of the season after hurting his knee during pregame warmups.

Poulin caught his skate in a rut in the crease and fell awkwardly Tuesday night moments before the opening faceoff against the Toronto Maple Leafs. An MRI exam Wednesday revealed a dislocated left knee cap that will require surgery and end the 20-year-old Poulin’s season.

The injury forced the Islanders to start Mikko Koskinen in his NHL debut, a 5-3 loss to the Maple Leafs. The Islanders didn’t have a backup goalie on the bench until the third period, when Joel Martin made it to Long Island from Bridgeport of the AHL.

They already were missing goalies Rick DiPietro (face, knee) and Nathan Lawson (knee).

The Islanders also say center Jeremy Colliton will be out for two weeks because of a rib injury sustained Tuesday.

DiPietro was placed on the injured list on Wednesday, and forward Jesse Joensuu was recalled from Bridgeport.