How old is old in rugby league? The question has been raised by Gareth Thomas’s switch from rugby union.

The former Wales and Lions rugby union captain, 35, will be officially confirmed on Friday as a Crusaders player, 24 hours after a bronze statue was unveiled in St Helens of a “veteran” league icon, Keiron Cunningham, who is 33 and will retire at the end of the season.

Thomas will be 36 in July — the same age as the oldest warhorse in the Engage Super League, Steve Menzies, the former Australia forward, now at Bradford Bulls — but in order to begin his switch immediately, Cardiff Blues, to whom Thomas was contracted until May, have apparently agreed to his early release, meaning that he has played his last game of union.

In Wrexham he will come under the wing of Iestyn Harris, the Crusaders assistant coach and his former Wales team-mate, who successfully moved from league to union. Thomas is the first big-name union international to cross to league since Scott Quinnell joined Wigan from Llanelli in 1994, the year before union went professional. The difference is that Quinnell was 21 when he converted.

“He’s at the wrong end of the scale at 35,” Quinnell said. “I couldn’t have imagined changing sports in my thirties. It’s difficult enough when you’re younger and you’ve time to learn. My worry is that they will want to play him every game because they have limited time with him.”

Nevertheless, the signing of Thomas signing represents a coup for Brian Noble, the Crusaders and former Great Britain coach, who has long championed a return to the signing of top union players. “A signing of his ilk will raise our profile some more,” Noble said. “We’ve already won some hearts and minds and we’ve got to show we’re an ambitious club.”

“I’ve looked at Welsh and English rugby union for a number of years and there are some great athletes who would enjoy our game. I hope it sends a message.”

Not that a union player taking up a new challenge in the twilight of a distinguished career will presage a flood into league, where the salary cap limits the scope for lavish spending. “I don’t feel 35 when I’m playing,” said Thomas, who is priced at 50-1 by one bookmaker to play for Wales in the 2013 Rugby League World Cup, when he will be 39.

Wigan Warriors, the only team with a 100 per cent league record after four matches, travel tonight to Bradford, where Paul Deacon is hoping for a sympathetic reception from the home fans on his return there, after appearances in six Grand Finals with the Bulls over 12 seasons.

Leeds Rhinos have the opportunity to get over the hangover of losing the World Club Challenge to Melbourne Storm at home to Harlequins, Hull host Castleford Tigers and Salford City Reds meet Catalans Dragons in a basement encounter at The Willows.