The father of former NRL star Nathan Merritt has told 7NEWS his son is extremely sick as he faces drug and gun charges.

Nathan Merritt revealed earlier this year he had around 12 months to live after being diagnosed with cancer.

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Police are now investigating the 43-year-old after linking him to a ram raid in the CBD this week.

Tony Merritt has been by his son’s side through the highs and the lows, from reaching the peak of the NRL to now fighting for his life.

“He might look good on the outside, but on the inside we know he’s very ill,” Tony Merritt said.

Nathan Merritt says he has just months to live, battling liver and oesophageal cancer.

“Trying to just maintain it now with chemo, I guess, and I try my best to try and stay alive as long as possible,” he said.

But now he’s fighting criminal charges too.

The former rugby league star’s Marrickville home was stormed by police on Thursday as detectives probed a ram raid on the high-end Fendi store in the CBD hours earlier.

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Police pounced on Merritt in his underground car park, led there as they pursued a vehicle linked to the store robbery.

Officers allegedly witnessed an interaction between Merritt and two men in the car.

“He’s done nothing wrong. It’s his unit. If people turn up in a unit in a car park, that’s their problem. It’s not Nathan’s problem,” Tony Merritt said.

A raid on Merritt’s home uncovered 12 grams of cocaine, which he says was for personal use, and a gel blaster bought on Facebook Marketplace for $100.

Merritt has not been charged over the ram raid, but did spend a night locked up in a police station for allegedly possessing illegal drugs and a pistol.

“I think it’s taken its toll on him,” his father said.

He was in court last month, cleared of a pub assault, saying afterwards it was time to focus on his health.

Merritt is effectively under house arrest while on bail, only allowed to leave home to report to Newtown police three times a week or to attend a medical appointment.

He’s due back in court in early November.