The Islanders’ toughest roster decision, at least for now, has been made for them.

Cal Ritchie will be sidelined for 1-2 weeks following a lower-body injury sustained in the preseason finale against the Flyers, as announced by the Isles on Friday.

With the NHL’s roster deadline for opening night set for Monday and the Islanders set to kick off their season on Thursday night in Pittsburgh, this essentially rules out the possibility of Ritchie, the 20-year-old prospect who has spent the past three weeks vigorously trying to secure a lineup spot against the Penguins, being included.

Despite a stellar training camp performance, it was always going to be unlikely for Ritchie to make the initial 23-man roster because there wasn’t a clear spot for him in the lineup.

The Islanders have four centermen in Bo Horvat, Mat Barzal, JG Pageau and Casey Cizikas, which would have blocked Ritchie from playing his natural position.

Barzal and Cizikas have both played wing as recently as last season, but the Islanders are committed to starting the season with Barzal playing in the middle, and moving Cizikas still would have displaced another NHL regular — possibly Max Tsyplakov — from the lineup.

Isles coach Patrick Roy said during camp that it was his preference to play Ritchie at center, though he can play on the wing as well.

In the preseason and training camp, Ritchie was used exclusively down the middle, with Roy often shuffling Cizikas to the wing as a result.

As for the possibility of using Ritchie as an extra forward, while the Islanders never explicitly ruled it out, it’s hard to see how that would have been better for his development than playing top-line minutes in the American Hockey League.

It also would have likely forced the Islanders to subject either Kyle MacLean or Marc Gatcomb, who are projected to start the season as the team’s two extra forwards, to waivers, where any team could have picked them up. Ritchie is waivers-exempt and can be sent to AHL Bridgeport with no risk.

While Roy publicly left the door open to the Islanders carrying eight defensemen earlier this week — which would mean waiving MacLean or Gatcomb to make room for Isaiah George — that does not seem to be a likely route for the club to take, given that George is also waivers exempt, and would also seemingly benefit more from playing every night than sitting in an NHL press box.

If the Islanders do indeed send George down to start the season in Bridgeport, it would mean that their 23-man roster is, in essence, set, though the short time frame on Ritchie’s injury all but guarantees it won’t be long before there is another decision to make.

Pierre Engvall’s looming return from hip surgery — Engvall has been skating on his own but has not rejoined the team for a practice as of yet — also has the potential to complicate matters.

Ritchie, who was subject to the CHL/NHL agreement while with the Ontario League’s Oshawa Generals, has never played in the AHL. He won an NHL job with the Avalanche in training camp last season, but played just seven games in Colorado before being returned to juniors. Assuming he starts off in Bridgeport, after returning from injury, it may not be long before he is knocking on the NHL’s door yet again.

Indeed, Ritchie would be the current betting favorite to be the Islanders’ first forward to be called up from Bridgeport, if the time frame given on his injury proves accurate. 

Ritchie’s health has removed what would have been Mathieu Darche’s toughest decision from his plate.

But that is very much a temporary situation.

Jonathan Drouin (illness) missed practice Friday.

The Islanders will spend the weekend on a team bonding trip in the Hamptons, practicing Sunday on Eastern Long Island before returning home.