Keighley Cougars and Wales rugby league player Danny Jones died from a cardiac arrest triggered by hereditary heart disease, a post-mortem has revealed.
Jones, 29, collapsed during a League One game at London Skolars on Sunday and was later pronounced dead in hospital.
The Rugby Football League said the problem was not revealed when Jones underwent an ECG scan in late 2014.
His wife Lizzie will attend the Cougars' home match on Sunday.
Jones won 12 Wales caps and scored over 1,000 points in 150 games over two spells with the West Yorkshire club.
"Whilst the findings of the post-mortem do provide an explanation for why he died, they allow for little comfort for Danny's family or all those who knew him," said Gary Fawcett, Keighley Cougars chief executive.
Jones was father to five-month-old twins Bobby and Phoebe, and a fund set up for Jones' family has already raised £77,000.
"His tragically premature death is still very painful for everyone, not least because his heart condition could not even be detected by the ECG," Fawcett added.
"All we can do now is mourn his passing, celebrate his life and do everything we can for Lizzie, their children and their wider family."