A teenager died from multiple organ failure three days after he succumbed to heatstroke during rugby league training in Perth, an inquest has heard.

Torran Jake Thomas, who was 190cm tall and weighed 122kg at age 15, had been pushing himself hard on the first day back at training with the West Coast Pirates junior academy following the Christmas break on January 5, 2015.

Torran Thomas.

Temperatures peaked at 44.4C at the Curtin Stadium in Bentley, but training went ahead in the evening after it had eased to 34.3C and there was a breeze.

The West Australian Coroners Court heard on Monday that players were advised via Facebook earlier in the day to drink plenty of water before training.