The Islanders’ hopes to upgrade their forward group this week took a bit of a blow on Wednesday when Steven Stamkos opted to stay in Tampa and signed an eight-year deal with the Lightning for an average of $8.5 million per season.

The Isles had reached out to Stamkos’ agents during the free-agent contact period, according to two people familiar with the conversation, and were planning to make a serious offer to the Lightning captain once the free-agency period opened on Friday at noon.

But Stamkos didn’t make it that far, choosing to stay with the Lightning to try and win his first Stanley Cup. The 26-year-old missed all of the last two months of the season except the last game of the Eastern Conference final with thoracic outlet syndrome.

Islanders general manager Garth Snow has had plenty of discussions with agents for a number of pending UFAs already, so his attention turns to changing his forward group with one or two players from among a decent but not overwhelming class of free agents.

There’s also the pending loss of two longtime Islander forwards, with Kyle Okposo — now perhaps the most attractive free-agent forward heading to Friday’s market with Stamkos signed — and Matt Martin both headed elsewhere.

Frans Nielsen is the Isles’ other big-name pending UFA. The Isles are believed to have made a strong offer to Nielsen but the 32-year-old center could also get some improved offers from teams like the Red Wings and Sabres, who were hoping to get a crack at Stamkos as well.

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Nielsen was at Martin’s youth hockey camp at Northwell Health Ice Center on Wednesday but declined comment on his situation.

In addition to Stamkos coming off the board, two big trades were made within minutes of one another that had tangential impact on the Isles.

The Oilers sent Taylor Hall to the Devils for young defenseman Adam Larsson and the Canadiens and Predators swapped headlining defensemen, with P.K. Subban going to Nashville and Shea Weber going to Montreal.

Subban and Weber were not in the Isles’ plans with the Isles already well-stocked on defense. But Hall had been on Snow’s radar for quite a while; it’s believed that the Oilers were offering Hall for Travis Hamonic earlier this year, when Hamonic’s trade request was still valid.

But since the Isles’ breakup day, when Hamonic rescinded that request, Hamonic became untouchable and the Isles had no other defenseman that matched Edmonton’s desires. So now Hall comes to a Metro Division rival, albeit one that has some holes in New Jersey.

Snow may also be scouring the trade market as teams add free agents and have to wrestle with salary-cap issues. The Lightning is now tighter to the cap and has some attractive forwards who could be moved, Alex Killorn among them.

With the possibility of losing some longtime veterans, Snow has a challenge this week. Without Stamkos, it just got a bit tougher.