"So if he keeps going like this, he's just going to drift and drift and drift.
"He'd be out of the top 100 now and pretty soon he'll be lucky to get into satellite tournaments."
Tomic conceded he had mental issues and was emotionally burned out after his Wimbledon loss to Mischa Zverev on Monday, saying he'd lost the motivation to perform even on sport's biggest stages.
Newcombe described the fallen star as a lost soul and said the former teenage prodigy was suffering from his decision to exile himself from Davis Cup.
"I've always found Bernie a nice, young bloke," said the former world men's No1.
"He's his own worst enemy. He's played some great Davis Cup matches for Australia. He elected not to play this year, so I think that was probably not good for him.
"[Being] around the team atmosphere probably would have been good for him.
"Unless he gets help and helps himself, nothing good is going to happen in the next 12 months."
A long-time patriarch of Australian tennis, Newcombe believes Tomic is delusional in believing he has a decade left on tour and also comparing himself to Roger Federer - as he bizarrely did when offering to return his prize money if the Swiss superstar did.
"If he keeps going like this, within a year he's going to hit complete rock bottom and he'll run out of money," Newcombe said.
"So when does the penny drop?"
Contrary to popular opinion, Newcombe also believes Tomic may benefit from a coaching reunion with his demanding and controversial father John, who has been assisting his tennis-playing daughter Sara.
"I don't know it personally, but I understand he's not having a lot to do with his father now and it's been a very authoritarian rule and maybe his father has to come back into the picture," he said.
"Maybe he'll respond to that.
"It's always a great shame when you see a talented young athlete destroying themselves.
"But it's his life. He makes his choices."
