TORONTO — The Knicks’ best laid plans may have gone up in smoke in one tragic moment Monday night.

The Knicks woke up Tuesday to the news of Kevin Durant’s feared torn Achilles tendon like the rest of New York — stunned.

Durant’s return from a calf strain turned into a catastrophe in the second quarter in Game 5 of the NBA Finals when he fell in a heap, ending his season — and maybe all of his next one.

It was 12:30 a.m. Tuesday when Warriors president Bob Myers entered the press conference room in tears to reveal the fear of an Achilles tear.

Now the cursed Knicks have to contemplate a free agency that may or may not include Durant, who could opt-in to the final $31 million year of his contract with the Warriors if he’s deemed out for next season.

According to a source, Durant has until the last possible day — June 29 — to make that decision. The courting begins a day earlier this year, June 30, and he still may be on crutches.

“KD could still get a max [deal],’’ said one NBA executive. “I think there’s a team that would take that chance for a player like him.’’

But instead of being the golden ticket, Durant is a risk. Durant visited a specialist in New York on Tuesday — which may be a sign of whether he still trusts Golden State’s medical staff.

Durant’s return from a 4½-week absence following a calf strain proved to be the wrong move. He went down early in the second quarter after playing just 11 minutes. Durant’s heartwarming Instagram message after the Game 5 victory, however, could be seen as an encouraging sign for the Warriors, who now trail the Raptors 3-2.

“I’m not sure he’ll now opt-in,’’ one NBA talent evaluator said. “He may feel it wasn’t smart [for the medical staff] to force him back.’’

Perhaps the Knicks weren’t clear-cut favorites to land Durant, as they were a couple of months ago, but they certainly had a strong chance with Durant’s agent and manager Rich Kleiman, a New York native, such an influential figure.

In recent weeks, it seemed Durant would not have Kyrie Irving as a partner to take the Knicks’ other max-salary slot. There were rumors floated by ESPN’s Stephen A. Smith that Irving even flew to San Francisco recently to convince Durant to join the Nets. Durant, however, may have believed he’s such a historic force, he could have come alone and made the Knicks great again.

Not anymore. Durant is no sure thing for anyone. Knicks president Steve Mills and general manager Scott Perry may have shed a tear along with Myers.

“It’s a bad basketball decision,’’ one NBA personnel director said. “It would be about ticket sales and fake goodwill, but that’s starting to be all used up.”

If an MRI exam confirms a full tear, Durant’s 2019-20 season could be over. An 8-to-12 month rehabilitation timetable is usually the norm.

If Durant does opt out, the Knicks and other suitors would be giving a soon-to-be 31-year-old his max deal, knowing some big men never recover fully from such a devastating leg injury. The 6-foot-9 Durant, who looked so good in that 11-point first quarter, may never be as dominant.

The only good news is — as The Post reported last week — Knicks officials fully expect a meeting with Kawhi Leonard. The star forward had the Raptors on the brink of a championship after scoring 10 straight points in the fourth quarter, but Toronto’s six-point lead evaporated in the final two and a half minutes of the 106-105 defeat.

Leonard lived in northern New Jersey with his uncle last season as he rehabbed from a quad injury and enjoyed it.

Broadcaster and former NFL receiver Cris Carter, who is a Leonard confidant, said it was possible for Leonard and Durant to hook up in New York. It may be tough for Durant to convince Leonard now.

On the free-agent landscape, point guard Kemba Walker has given off heavy vibes he’s happy in Charlotte, where all the money is. The Knicks never made a single inquiry about Jimmy Butler when he was on the trading block, so it doesn’t appear they consider him a franchise-changer in the way Leonard is and Durant was.

There are second-tier free agents to consider, however, such as Pelicans power forward Julius Randle, whom the Knicks like and who plays their neediest position.

The Knicks also could trade several young assets, including their No. 3 pick, which could turn into RJ Barrett, for Randle’s Pelicans teammate, Anthony Davis. But even if they do, it may not even make them a playoff team if Davis doesn’t have a star partner.

According to a source, the Pelicans would need a third team in a trade with the Knicks more than in a deal with any other potential club in the mix. Pelicans brass doesn’t find all the Knicks’ young assets attractive enough for a package.

The Pelicans want an All-Star player involved in a deal, but New Orleans also desperately seeks a young, potential top-15 guy and don’t know if the Knicks actually have one on their roster.

Kevin Knox is the closest to a potential All-Star, but he went through a roller-coaster rookie season. According to a source, the Pelicans consider the Celtics to have the best young assets.

The Knicks can still use their cap space to acquire another star player, aside from Davis, in a trade.

Nevertheless, maybe the answer is for the Knicks to continue a slow rebuilding, draft Barrett, tank in 2019-20, add another lottery pick and go after Durant in 2020 if available.