The Nets just lost the one player they couldn’t afford to lose.

Now, it remains to be seen how long until they get back D’Angelo Russell.

The point guard was forced out of Thursday’s 110-97 loss to the Cavaliers at Barclays Center with a right ankle sprain and didn’t return.

Since Russell joined the Nets, they entered the Cavs tilt 8-8 when he played but 0-6 when he didn’t. That’s inauspicious.

On Thursday, the floor leader showcased their influence once more, guiding the Nets to a 60-55 lead against Cleveland, a team currently tied for the best record in the NBA.

But he hopped off the floor with 8:39 left in the third quarter and never came back.

Neither did the Nets’ momentum.

Keon Johnson (16 points) immediately committed a turnover, and the Nets conceded an extended 28-11 run to fall behind by 12.

The Nets shot just 5 of 15 with three turnovers during that blitz, the misses and giveaways fueling Cleveland’s transition game.

They also allowed 11-of-15 shooting to the visitors, with Donovan Mitchell (game-high 26 points) hitting a pull-up 3 to make it 83-71 with a minute left in the third.

The deficit swelled to 20 in the fourth.

Cam Johnson had a team-high 18.

But without Russell — who finished with three points and a team-high five assists — the attack sputtered.

Even Cleveland’s Kenny Atkinson — who coached Russell in his first Nets go-around — noted before the game the guard’s importance.

“DLo is at the center of it,” Atkinson said. “He’s a natural leader. He has natural charisma. I used to say with the Nets, he’s got star charisma. He really does. Whatever that DNA is, DLo, you can have your opinion about him, but DLo thinks he’s a star, knows he’s a star, and I love that about him.

“He must be in the perfect place now, right? He’s kinda seen it all. He’s at that age where I assume he’s the alpha in that locker room. I’m just a big fan of the player, big fan of the leader, big fan of the person.”

The Nets have had a gaping hole at backup point guard behind Russell ever since buying out Ben Simmons, and they had been forced to use forward Trendon Watford there.

They gave Killian Hayes — who had been toiling with G-League Long Island — a 10-day contract to try out for that role.

Now, he could be forced into an even heavier workload.

“Trendon can be the guy that you know runs the point guard, but at the same time, Trendon can be a 1, 2, 3, he’s multi-positional. So having a quote-unquote more like a traditional backup point guard also is good for us,” coach Jordi Fernandez said. “Give it a look, this 10-day is important, not just for him, but also for us. And he can do the things we ask him to do, we know who he is. That’s the reason why we brought him in the first place.”