OAKLAND, Calif. — Warriors backup point guard Quinn Cook has known Kevin Durant since the injured superstar was an unknown, skinny teenager in Seat Pleasant, Md., and he’s not going to doubt his friend now.

Amid widespread speculation Durant will never be the same player after rupturing his Achilles tendon Monday night during Game 5 of the NBA Finals, Cook gave a much more encouraging outlook — and one that is sure to warm the hearts of Knicks fans.

The Post reported Wednesday the Knicks aren’t backing off from pursuing Durant, a free agent on June 30. Achilles tendon tears are historically the most difficult injury to come back from for big men and Durant is expected to miss the 2019-20 season, ESPN confirmed.

“He’s going to come back 10 times better,’’ Cook told The Post ahead of Thursday’s Game 6. “That’s what kind of a person he is. The only thing about his future, Kevin Durant is going to be back 10 times better than ever. There’s no question about that. He’s not going to be the same player. He’s going to be better.”

Cook is one of Durant’s closest friends. The two played together in the AAU system in Maryland. As Warriors teammates, they live together and their lockers are side by side. Despite his sunny prognosis, Cook can’t believe Durant could be robbed of a full year of his prime.

“I’m sick to my stomach, hurt and heartbroken,’’ Cook said. “Your teammates and he’s put his heart and soul into the team, into his craft. He worked so hard, worked his ass off to get back. That lift he gave us — those 11 points [in the first quarter Monday], he gave us a boost we needed. I wish he was here with us. That’s our motivation right now.

“The focus is winning the championship for him, the city, the organization.”

Durant, who had been out with a calf strain suffered in the Western Conference semifinals, returned to supply 11 first-quarter points Monday, hitting two 3s, but he went down in a heap after making a move on Serge Ibaka early in the second quarter. He was helped by teammates off the court — perhaps not to return until the start of the 2020-21 season.

“Being off 33 days and to do that, in an elimination game on the road in the NBA Finals, to do what he did in those 12 minutes he played, that’s testament to who he is and the type of person,’’ Cook said. “He put his body on the line for us.”

The Warriors

pulled out a 106-105 victory

and Durant was there for his team at halftime despite already being on crutches and with everyone knowing his sad fate.

“He gave us all the strength we needed at halftime, everything we needed to win the game in the second half,’’ said Cook, who played at Duke. “It was emotional. We didn’t need a speech. His presence was enough. Everyone gave him a hug, everyone loves him. His presence was all we needed. He gave us a spark in the second half.’’

Durant’s injury put an extra onus on the Warriors’ bench to pull out the series, as they trailed 3-2 entering Thursday. Cook is a 3-point specialist who had hit them at 35.7 percent (5 of 14) in the first five games.

Durant wasn’t on hand Thursday at Oracle Arena after undergoing surgery Wednesday in New York at the Hospital for Special Surgery. Speculation some teammates were confused why Durant hadn’t returned yet from a calf strain eats at Cook. Those in the media questioning Durant’s unwillingness to return seem silly now.

“It was false,’’ Cook said. “Fans don’t know what’s going on in locker room and rehab, stuff they don’t see. We were behind him 110 percent, not rushing him. We all got excited when he started doing core work. He was trying to come back as soon as possible.’’

All-Star shooting guard Klay Thompson was absolutely miffed a notion existed the Warriors were better without Durant and didn’t need his 11-points-in-12-minutes burst to prove it.

“If anyone watched the last three years of basketball, you saw this man was the Finals MVP back to back,’’ Thompson said. “So those talking heads who say we’re better without him, that’s just ludicrous. Like that’s crazy. This is the best player in the world. You could put him on the 30th best team in the league, and that team will make the playoffs. That’s how talented he is.

“Without him we’re a really good team, but it’s, you throw Kevin Durant out there, like I said before, one of the greatest ever.”

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