ATLANTA — The beef between Ben Simmons and his former Philadelphia team just got a new wrinkle and another layer. As the All-Star fights to get back to playing, he’ll also be fighting to get his back pay.

The Nets’ injured All-Star has filed a grievance to recoup the nearly $20 million of salary that the 76ers withheld from him, according to ESPN. It sets up what could be a huge showdown, now going into an arbitration process with the NBPA backing Simmons — still looking to make his Nets debut.

“He’s doing some light shooting, so he’s on the court a little bit the past couple days, but nothing dynamic,” coach Steve Nash said, confirming Simmons isn’t even up to one-on-zero work yet. “He’s not even moving around a lot. He’s just doing some light shooting.”

Simmons was the centerpiece of the Nets’ Feb. 10 deal with Philadelphia, but he is dealing with a herniated L-4 disc and still hasn’t been cleared for practice.

The All-Star did travel with the Nets to Atlanta — a second consecutive road game, after having not taken a flight since the Feb. 26 tilt in Milwaukee — and recently resumed light on-court work, taking part in pregame walkthroughs trying to return in time for the play-in. But sources told The Post he’s still several steps away.

“He hasn’t really practiced with us. He really just passes the ball,” said Bruce Brown. “I don’t think he’s done much.”

Meanwhile, as Simmons tries to ramp up, he’s also trying to recoup his salary.

After Simmons and agent Rich Paul of Klutch Sports asked the 76ers for a trade this offseason, he held out citing mental health issues and said he wasn’t ready to play.

Simmons saw a therapist, and Sixers GM Daryl Morey told the “Rights to Ricky Sanchez” podcast that he believed his star was telling the truth about his issues.

“To be fair to him, he clearly — I believe him. He was going through something,” Morey admitted at the time. “And it was just whether or not we could’ve gotten to the point where we’d have him play basketball for us. I should’ve had a better relationship with Ben. I really believe that. That’s on me.”

But now Philadelphia has claimed Simmons was in breach of his contract under the collective bargaining agreement between the league and the NBPA. As such, the 76ers contended they had the right to recoup the salary advanced to Simmons before this season.

The 76ers had been withholding nearly $1.3 million of Simmons’ salary in each paycheck, which has continued since the trade to the Nets, who were made to deduct salary to wire to the 76ers, according to ESPN.

In essence, Simmons has been fined almost $20 million for games ($360,000 per) that he missed in Philadelphia. Since he got $16.5 million in advance, and he’s on a six-month pay cycle (from Nov. 15 to April 30), there isn’t enough in each paycheck to cover the loss.

Simmons and Paul had multiple discussions with the Sixers since the Feb. 10 blockbuster, but when those talks broke down with no resolution, the grievance was filed with the Sixers, NBA and NBPA late this week.

Meanwhile, Simmons still isn’t cleared to even practice for the Nets. He was ramping up to play when he suffered his fourth back injury in the last two years.

Simmons had missed eight straight games and was getting treatment for nerve issues in his lower back when the 2019-20 campaign was halted by COVID-19. The next season, he suffered nerve impingement in his lower back severe enough to induce vomiting, then had a flare-up earlier this season.

The back issue and relevant scans were all disclosed during the trade talks and didn’t pose any significant long-term issues for the Nets, according to ESPN. But after the latest flare-up, Simmons got an epidural injection while the Nets were in Orlando for a Feb. 15 game.

Now as he seeks to get back on court, he’ll also be looking to recoup his salary.