Ben Simmons has impressed the Nets with his renewed athleticism and aggressiveness for much of the pre-season, but there are a few things his old coach said he needs to see before he’s ready to say the former All-Star is back.

“He’s looked healthy,’’ Doc Rivers said Saturday (all times AEDT) of the player he coached with the 76ers. “That’s the No. 1 thing that Ben had to be — and then the mental health part of it as well.”

With Simmons seemingly feeling good both on and off the court, Rivers said the next step will involve a part of his game that has typically haunted the 6-foot-10 star.

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“For me, the one thing he has to be able to do is make free throws,’’ said Rivers said, whose three-year tenure as Philadelphia’s head coach ended after last season.

“I never worried about his jump shot or any of that stuff because I really believe the free throws are the key that unlocks everything for him.”

And if Simmons does that — he’s 4-for-7 from the line so far this pre-season — Rivers, now back with ESPN as an NBA broadcaster, believes he can get back to playing at a high level.

“Listen, I coached Ben for one year, and he had one of the best seasons of his career,’’ Rivers said of the 2020-21 season, when Simmons was an All-Star for a third straight year.

“I still think Ben, when playing right, has a chance to be an All-Star player.”

But “playing right,” according to Rivers, means different things to different people when it comes to Simmons.

“I think every coach that has coached him has their version of what we think, for Ben, is playing right,’’ Rivers said. “And then, it’s everybody else.”

Rivers, of course, famously said after that 2020-21 season that he didn’t know if a team could win a title with Simmons at point guard due to his offensive limitations.

The Nets still have to find out just what version they’re getting of the 27-year-old Simmons.

He was strong and played well in the team’s first three pre-season games, but was less impressive in their final game against the Heat, with Simmons going 0-for-4 from the field and scoring just two points.

The point guard still managed to contribute seven assists and eight rebounds in the win.

“He’s so physical and can get to the basket and drive and attack the basket, (along) with his passing ability, he can really dominate the game from that position,’’ Rivers said.

Rivers then brought up parallels between Simmons and Magic Johnson, a comparison he has made before.

“He’s so similar, and I hate to put this category on him, (but) he’s so similar to Magic in a lot of ways, as far as his passing ability, his size,” Rivers said. “He has great vision, and with that and him being aggressive towards the basket, if he’s healthy, I think he has a chance to restore himself.”

Simmons told The Post’s Brian Lewis this week: “I’m going to be better than I was.”

At this point the Nets, who owe Simmons $77 million over the next two seasons, would take his former skill level.

If he loses a step, he won’t be able to demonstrate the parts of his game that made him unique.

“If he can come back with his athleticism and speed and power, Ben Simmons going downhill is a problem,’’ Rivers said. “But he has to be healthy. He has to have his burst back. And that’s the only thing I wonder is if he can have that. If he can’t have that, then he has to create another way of playing, and that’s gonna be hard.”

-This story was originally published in The New York Post and reproduced with permission.