The former Carolina Panthers quarterback sent the message loud and clear on his "4th & 1 with Cam Newton" podcast this week ... going off on Rice for around five minutes over the recent decisions that have led to police investigations.

Newton advised the wide receiver to lay as low as possible going forward ... explaining that's the only way he can now guarantee himself the best possibility at a long-term future in the NFL.

"I will tell you this," Newton said in part of his speech, "It's not a person in the NFL, Patrick Mahomes included, the league don't need you, bro. Trust me. They do not need you."

Rice first found himself in the crosshairs of authorities in March -- after he drove one of the two luxury cars that caused a massive pileup on a Texas highway. Weeks later, cops looked into him yet again, after he was accused of hitting a photographer outside of a nightclub.

Newton ripped the 24-year-old for putting himself in the situations that led to those police probes ... and warned him to "sit your ass down somewhere, bro."

"You're too loud right now, bro," the three-time Pro Bowler said. "What you want to do?"

"You can do that s*** out the way. Keep that s*** in perspective. Keep the main thing the main thing."

Newton also dragged Rice's inner circle for not helping him navigate everything ... pinning almost all of the blame for his recent troubles on those closest to the K.C. receiver.

"He's f***ing it up," Newton said, "and it's because of the supporting cast."

Cam went on to say, though, he doesn't think it's too late ... if Rice can somehow figure out how to keep the heat off him in the near future.