Williams, 27, had made six appearances for the Championship club this season after joining from Rotherham Titans last summer.

"It is with great sadness that Doncaster RFC announces the passing of prop forward Ian Williams," a statement on the club's website read.

"Ian collapsed at training at Castle Park this morning and, despite the best efforts of the emergency response team, could not be resuscitated.

"We extend our deepest sympathies to Ian's mother Pippa, father Phillip & and sister Helen and are working with a counselling team in the best interest of Ian's teammates."

Oxford graduate Williams played in the 2013 Varsity match and also had spells with London Welsh and Richmond.