Kato Ottio was attempting to inspire his young Papua New Guinea teammates when he collapsed and later died in a tragedy that has broken the heart of rugby league.
The 23-year-old's manager Steve Deacon told Wide World of Sports that Ottio had completed an 8km run with other players from the Hunters Queensland Cup team in his homeland when he made a fateful decision.
"The run was over and a few of the boys walked back while others got a ride," Deacon said.
"But Kato told a few of the players 'let's run back'. He wanted to use the professionalism he gained from his time at Canberra to rub off on his younger countrymen.
"He got slower and eventually collapsed. He was unconscious and in a coma and they were not able to revive him."
Ottio's mother, Joyce, said doctors told her that her son had suffered severe heatstroke. "He should be close to me and my family," she told The Daily Telegraph from PNG.
"He got heatstroke, that's what the doctor said. I love him so much, he is my everything. I was with him at the hospital and he should be close to me, I miss my son so much."
English team Widnes Vikings announced Ottio's death, saying he was due to fly to the UK this week to play in the upcoming Super League.
Ottio signed for Widnes at the end of last year from Australian National Rugby League team the Canberra Raiders.
Widnes says Ottio "developed a sudden health issue while training" on Sunday.
Ottio was a winger in the Papua New Guinea side that won its group at the World Cup before losing to England in the quarterfinals.
Widnes coach Denis Betts says "all of us saw at the World Cup the incredible gifts that Kato had, and his potential to forge a great career in rugby league".
- With AP