Adam Pelech was warming up for a game against the Canucks on Jan. 17, a few days after the 21-year-old defenseman had two assists in an Islanders’ win over the Rangers. Things could not have been going better for Pelech, who in just seven games had shown himself to be a surprisingly calm and patient NHLer.

Within minutes, things went seriously wrong.

“My right side started swelling up, there was some tightness and kind of a bluish-purplish color,” Pelech told Newsday on Tuesday. “I went to the trainers and they felt it could have been a blood clot, since those are some of the symptoms. I went to a hospital in Brooklyn, they did an ultrasound and showed it was a clot, so I went to North Shore [University Hospital] in Long Island for a few more days of tests.”

And just like that, a promising first NHL season appeared over — or even more than that. But after a week or so without a firm diagnosis, Pelech was found to have thoracic outlet syndrome, a compression of the blood vessels running from the upper body to the arms.

Now, following surgery in California to remove part of the uppermost rib and some muscle on Pelech’s right side, he’s ready to resume his season. He’ll play for Bridgeport this weekend and, incredibly, could be a real option for Jack Capuano and the Islanders in the playoffs, which start next week.

“That would be amazing,” he said. “If you’d told me when it happened I might have a chance to play in the playoffs this year, it’d be hard to believe.”

Pelech credits the Islanders’ medical training staff, which reached out immediately to its counterparts with the Bruins and Lightning — Bruins defenseman Adam McQuaid and Lightning goaltender Andrei Vasilevskiy both had TOS and returned to play.

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Pelech’s oldest brother, Matt, also dealt with a similar issue six years ago. “I was on the phone with him every day and he helped me get through the recovery,” Adam said.

And he credits Dr. Julie Freischlag and her team at UC-Davis for allowing Pelech to believe he’d be back playing again, even this season. “She said she does these surgeries for athletes all the time,” he said. “It calmed me down quite a bit.”

With Travis Hamonic out indefinitely, the Islanders’ defense will be stretched thin if they can qualify for the postseason this final week. And Pelech’s return could be a huge boost.