John Tavares poses with Maple Leafs president Brendan Shanahan, left,...

John Tavares poses with Maple Leafs president Brendan Shanahan, left, and general manager Kyle Dubas following a news conference in Toronto on Sunday. Credit: The Canadian Press via AP / Chris Young

It’s time for the Islanders’ Plan B.

And that clearly is looking to improve via the trade market rather than through free agency. The free-agent cupboard is relatively empty at this point.

The Islanders lost the top player on the market, their own John Tavares, to his hometown Toronto Maple Leafs on Sunday. Shortly after the free-agent market opened at noon, their franchise player, selected first overall in 2009, agreed to a seven-year, $77-million deal.

Since then, new president Lou Lamoriello has made some depth signings to shore up the penalty kill and Bridgeport (AHL) roster but has yet to address his non-Tavares top offseason priorities.

The Islanders need a No. 1 goalie. After allowing an NHL-high 293 goals, they need to shore up their defense corps even after re-signing valuable Thomas Hickey.

Plus, with Tavares off to Toronto, the Islanders suddenly are short an experienced No. 1 center, let alone a captain.

The Islanders have more than $20 million in salary-cap space after dipping into free agency to sign bottom-six forwards Tom Kuhnhackl (Penguins), Leo Komarov (Maple Leafs) and Valtteri Filppula (Flyers).

Calvin de Haan, selected 12th overall by the Islanders in 2009, likely is the most attractive defenseman still available as a free agent and has attracted plenty of attention. A shoulder injury limited him to 33 games with the Islanders last season. He would be valuable to them in a top-four role, but the expectation is he will sign elsewhere.

The market for defensemen could include two-time Norris Trophy winner Erik Karlsson, 28. The Senators said on Monday that they have offered him an undisclosed extension, but there’s no indication whether he is willing to re-sign with the team that drafted him 15th overall in 2008.

That could put the Senators in the same situation the Islanders were in with Tavares, who became eligible to sign an extension on July 1, 2017. The uncertainty about whether he would return lingered throughout the season, and after opting not to deal him at the trade deadline, the Islanders wound up losing him for nothing. No doubt, Ottawa is mindful of the Islanders’ example.

The Kings’ Drew Doughty, 28, the second overall pick in 2008, just set the bar for defensemen contracts by signing an eight-year, $88-million extension on Sunday.

To deal Karlsson, the Senators might look to package him with right wing Bobby Ryan, 31, in order to dump the final four seasons of his seven-year, $50.75-million deal.

The Senators undoubtedly would be looking to acquire at least one first-round pick as well as prospects and likely NHL-ready players in a deal for Karlsson. The Islanders just took two defensemen, Noah Dobson at No. 12 and Bode Wilde at No. 41, among their top three picks.

Ottawa is believed to be shopping goalie Craig Anderson, 37, entering a two-year, $9.5-million extension.

The Sabres’ Robin Lehner is an unrestricted free agent but free-agent goalies Carter Hutton (Blues), Jonathan Bernier (Red Wings) and Cam Ward (Blackhawks) have found homes.

The market for centers is thin after Paul Stastny left the Jets for a three-year, $19.5-million deal with Vegas and the Sabres traded Ryan O’Reilly to the Blues for Patrik Berglund, Vladimir Sobotka, Tage Thompson and first- and second-round picks.

Mathew Barzal, who won the Calder Trophy as the NHL’s top rookie, might be thrust into a top-line role for the Islanders. Fellow 21-year-old Anthony Beauvillier could be switched from left wing to the middle.

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