The defenceman will undergo a heart procedure on Tuesday and will be out indefinitely, the team announced.
Reilly, 31, has been out of the lineup since suffering a concussion on Nov. 1 in Buffalo. During routine post-concussion tests, the heart condition was discovered. The condition is unrelated to the injury he suffered.
“It’s probably a blessing in disguise of what transpired,” Islanders President of Hockey Ops and General Manager Lou Lamoriello said in a statement. “They detected this, something that you’re sometimes born with but never knew.
“[His quality of life will be] 100 per cent and he will be able to play once this procedure is done.”
Despite the team saying that he’ll be able to continue his hockey career following the surgery, they did not release a definitive timeline for a return.
The left-shot blueliner is in his second season with the Islanders after being claimed off waivers from Boston last season. Reilly signed a one-year $1.25 million contract to remain with the club.
He had six goals and 18 assists in 59 games last season for New York, but is pointless in 11 games this year.
In more Islanders injury news, fellow defenceman Alexander Romanov participated in his second consecutive practice Monday as is a “game-time decision” for Tuesday’s matchup in Calgary, per head coach Patrick Roy.
Anthony Duclair, Mathew Barzal and Adam Pelech have all yet to resume skating.
After facing the Flames, the Islanders play Detroit on Thursday.
