While the Nets and Knicks have tantalized Kevin Durant, neither franchise can offer him that golden year — a fifth season paying $50 million.

It’s the one carrot that keeps the Warriors in play as Durant weighs his options with free agency beginning Sunday night.

With Durant coming off Achilles tendon surgery, one NBA executive and one Achilles specialist said they believe long-term compensation should rise as a stronger consideration. Durant will be 32 when he debuts for his new/old team — in 2020-21.

A leading Achilles expert, Dr. Anish Kadakia, of Northwestern University, has reviewed studies showing 85% of NBA players who suffer Achilles tendon ruptures don’t last more than two seasons after their return.

According to Kadakia, 68% return and 32% never play again. Further, it takes until the second season back for the player to return to his normal ability, taking into consideration “aged matched controls,” he said.

“Very few players play past two seasons,’’ Kadakia told The Post. “Two seasons and that’s it. But after two years and you’re still playing, studies show you’ll be as good as you’d be as if you didn’t rupture — factoring in decline with age. You probably haven’t lost anything but time. But in three years, it’s not the same Durant from three weeks ago.”

As The Post reported Friday, the Knicks will proceed cautiously, hoping to view medical records before signing off. But that could also create issues if there’s a red flag in Durant’s physical. The Knicks could look to call off a deal, but other free agents may have signed up.

Kadakia said in the first season back, which would be 2020-21, Durant won’t be the same athletic player. Scarring and atrophy of the muscle causes slippage.

However, the Achilles specialist said a new surgery technique called “Arthrex PARS speed bridge” results in less scarring, considered a breakthrough.

“Why would you not go back to the Warriors if winning is important to you and make that extra 50?’’ a neutral NBA executive told The Post. “At his age, take the five years if you could get it. He’s got a winning program. That’s a lot of money. Awful lot of money. He’s not saying I have too much money.

“With Kevin, Klay [Thompson], Steph [Curry], a new arena, great city, holy cow,’’ the executive added. “They can talk about more marketing money in New York, but these are global guys. Kevin and Kawhi [Leonard] are global guys. Their names are gold regardless if it’s smaller market, bigger market. And Silicon Valley is a big deal, too.’’

In all, Golden State’s offer can top the Knicks or Nets by $57 million. The Warriors’ max is five years, $221 million. Other teams can offer a max of just four years, $164 million.

Durant, out next season, can always sign with the Warriors for the money and request a trade to New York at a later date. Meanwhile, the Nets have emerged as betting favorite in Las Vegas.

In explaining why Durant won’t be the same sniper in 2020-21, Kadakia said it’s jumping and speed. The surgically repaired leg regains just 95 percent of the power of the healthy leg.

“When you shoot, you jump,” he said. “You’re jump is off because you don’t have as much power in one leg than the other. You play your whole career based on how much height and quick reaction you get when you want to shoot. Some can’t do that anymore, no longer able to push off like you were before.

“And speed is heavily affected, making the quick cut. You lose a little of that power, when you want to push off as hard as you want. An elite athlete losing 5 percent power makes big difference.’’

According to a Durant confidant, ESPN’s Jay Williams, Durant is not planning to stage elaborate meetings with teams, like he did in 2016 at the Hamptons. Just phone calls.

Durant is still being pictured in New York moving about with a handheld motorized scooter, sporting an orange cast. A source told The Post Durant’s recovery from surgery still has taken a mental and physical drain – which would make face-to-face meetings less enjoyable.