The Islanders will return to the renovated Nassau Coliseum to play a preseason game, marking the team’s first time back since leaving two years ago.

The exhibition game is scheduled for Sunday, Sept. 17, at 1 p.m. against the Philadelphia Flyers. It will be the Islanders’ only appearance next season at the team’s former home, which means the arena operator will owe Nassau County $1 million for not meeting a clause that called for two preseason and four regular season games, a spokesman for Nassau Executive Edward Mangano said Thursday.

“They are contractually obligated and the penalty will be fully enforced,” Mangano spokesman Brian Nevin said.

The 2013 arena lease between Nassau County and Nassau Events Center — a subsidiary of Brooklyn Sports & Entertainment that also operates Barclays Center — stipulates that if the Islanders “are unable or unwilling” to play the games, NEC will have to pay Nassau an additional $1 million annually.

The games were a major selling point with Nassau County officials in the NEC’s bid against Madison Square Garden to renovate and manage the Coliseum.

When Newsday reported last month that the Islanders would not be playing any regular-season games at the Coliseum next season, Mangano declined to say then whether the county would enforce the terms.

But after the announcement of the Islanders’ lone exhibition game at the Coliseum became official Thursday in a news release from Brooklyn Sports & Entertainment, Nevin said the county executive “100 percent” intends to make NEC pay the penalty.

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Nassau Events Center declined to comment.

The announcement comes as the Islanders’ future home remains in flux. The team is engaged in negotiations with Barclays management over the terms of their 25-year agreement as it awaits the state to release a request for proposals to develop the land next to Belmont Park.

The Islanders, who last played at the Coliseum on April 25, 2015, are expected to propose a new arena at Belmont. Both the Islanders and Barclays Center can opt out of their 25-year arena deal next January. They recently finished their second season together.

Tickets for the preseason game at the Coliseum go on sale June 29. As part of the terms of the Islanders’ arena deal with Barclays Center, all ticket revenue for preseason and regular-season games — along with other line items such as concessions, advertising and marketing — goes to Barclays Center in exchange for an annual rate of $55 million. But that amount can be reduced based on a number of factors, including operating costs of the arena.

Most recent publicly available financial disclosure figures show Barclays Center paid the Islanders $37.5 million for the 2015-16 season, the Islanders’ first at the Brooklyn arena.