Johnny Boychuk will miss the next four to six weeks with an upper-body injury, the Islanders announced Monday, and the defense will be seriously tested during this crucial stretch of the season.

Boychuk suffered his injury, believed to be a left shoulder problem, on Thursday night in Buffalo. He moved to hit Sabres rookie Jack Eichel, missed and plowed into the end boards shoulder first. Boychuk immediately left the ice and was placed on injured reserve the next day.

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He does not need surgery. Perhaps the only other bit of good news: The Islanders have an eight-day break for the NHL All-Star Game during Boychuk’s absence and he could be close to returning when they resume play Feb. 2.

The defenseman, who will be 32 this month, has three goals and 11 assists and formed a strong second-defense pair with Calvin de Haan after his pairing with Nick Leddy, the Isles’ top pair all last season, fizzled a bit to start 2015-16.

Boychuk also led all Islanders with 2:45 of shorthanded ice time per game. The Isles’ streak of consecutive penalty kills ended at 42 just before Boychuk was hurt Thursday. It may be a coincidence, but in the two games Boychuk already has missed, the Islanders have allowed three power-play goals in eight times short.

The Islanders could look to the trade market to find a veteran to help shore up their defensive depth, but that market is flooded with teams seeking upgrades. Travis Hamonic had requested a trade before the start of the season, but he won’t be moved now that Boychuk is out. If anything, the Isles would want to add on defense, not shuffle around their top four.

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Adam Pelech, recalled from Bridgeport on Friday, had a strong game while paired with de Haan in Sunday’s 6-5 win over the Stars. Ryan Pulock and Scott Mayfield remain in Bridgeport as other internal options.