On the way home from hospital for lingering headaches, George Diamond told his dad he was being overprotective and needed to have more faith in the doctors treating him.
Two months later, the 18-year-old boxer died at the Alfred Hospital in Melbourne from bleeding near his brain, with an autopsy revealing an older subdural haemorrhage.
An inquest investigating the links between the head knock Mr Diamond suffered in October 2018 and his death on February 2019 after collapsing at the Sting Gym found doctors missed several opportunities to detect the bleed as they did not order brain scans despite his ongoing symptoms.
Mr Diamond visited two GPs with his father after being punched in the groin and head at the Cranbourne West gym on October 25.
Both doctors sent him away without ordering a CT scan or MRI.
Mr Diamond was prescribed Panadol and Nurofen after visiting Dr Pejman Hajbabaie, who noted his head injury was not getting better, six days after visiting another GP.
When Mr Diamond's symptoms persisted his father, Vic Diamond, took him to Frankston Hospital on November 5, begging emergency physician Dr Yigal Reuben for a CT scan or MRI for his son.
Dr Reuben diagnosed Mr Diamond with concussion but said the scans were unnecessary and recommended against playing sport while the symptoms continued.
Vic Diamond said he will live with the regret of not taking his son to a fourth medical professional.
"On the way home, I said to him, 'maybe, Georgie, just give boxing a rest for a little while'," Vic Diamond told AAP.
But his son told him the trainers at the gym and the multiple doctors had cleared him.
"You're being overprotective. We need to put some faith in what the doctors are saying," he told his dad.
The teenager was medically suspended from the Sting Gym after the October concussion but returned to regular training in late December 2018 or early January 2019, before increasing his intensity after receiving a certificate of fitness from Dr Hajbabaie.
On February 18, 2019, Mr Diamond collapsed at the gym and died in hospital three days later.
Coroner John Cain on Monday delivered his findings that Dr Hajbabaie and Dr Reuben should have ordered Mr Diamond to undergo a CT scan on multiple occasions.
"Had a CT scan been undertaken on 5 November 2018, it is more likely than not that it would have revealed that George had a subdural haematoma," he said.
He also found Dr Hajbabaie's note-keeping of his two appointments in October 2018 and January 2019 fell well below standard, which contributed to his decision to sign off Mr Diamond's return to boxing despite his lingering symptoms.
"The parent's opinion has to matter when it comes to the welfare and the health of their own child," Vic Diamond said.
The boxer's mother Shayla remembers him as a caring and happy person who was there to support others in tough times, opting to go live with his elderly grandpa after his grandma had died.
"It's a very big loss - from my dad to our youngest son, all of us - it's been a complete horrific nightmare," she said.
The coroner recommended there be more stringent requirements for individuals to be cleared before commencing amateur combat sports for the first time and before returning following injury.
He urged the peak bodies representing neurosurgical, GP, and sports and exercise doctors develop mandatory training in medical clearance for people beginning or returning from injury to combat sports and guidelines on the appropriate threshold for undertaking brain CT scan or MRI following a boxing or mixed martial arts injury.
