Hayne's bombshell announcement that he was quitting the NRL did not shock Stuart, who oversaw the Eels star's previous contract extension at Parramatta last year.

"When we re-signed him, we offered him a longer term deal of four or five years, but he said 'I'm probably looking towards a break or challenging myself in some other area in a couple of years, so I don't want to commit too long'," Stuart said. "So it hasn't been a great surprise to me ... it's always been something in his heart, now he's made the decision to pursue it."

While Stuart backed Hayne's courage and athleticism to trial for the NFL, the former NSW Origin and Australia coach admitted to concerns that players in their prime were leaving for other sporting challenges.

Sam Burgess, 25, and Sonny Bill Williams, 29, have each played starring roles in the past two NRL premierships, but are leaving in bids to play at next year's rugby union World Cup.

NRL boss David Smith was prepared to use his marquee player discretion powers to try and keep Hayne in league, but the Eels fullback could not be swayed by money.

"In my opinion only, it is a concern because they're all going for a bigger stage: two players for World Cups and Jarryd trying to make a name in the big arena of the NFL," Stuart said. "But what do you do? It's like being an actor on Home and Away and Hollywood looks at you. What can the league do?

"When you've got guys wanting to play in a World Cup, you've got Jarryd going to one of the biggest sporting arenas in the world, you've got to applaud them for having the ability and capacity to be able to do it.

"Jarryd's not money driven, he really is a guy that's driven by the challenge and the big stage. He always performs well in big games, in the big environments. Nothing's going to change, he's going to have a good opportunity to prove himself there."

Hayne, 26, is the current Dally M medallist at the top of his game, but Stuart said that meant it was now or never for him to pursue his NFL dream.

"The timing of it is right for him, physically," Stuart said. "The last two years is the fittest I've seen him ... if he's going to want to take this challenge up it's better to do it when he's at the top of his form.

"With his athletic ability, his explosion, power and speed, he will certainly be up there with some of the athletes at NFL level I'd assume. I've worked with some good athletes in rugby league and Jarryd's athletic ability is certainly up at the top."

Stuart experienced the gamble of crossing codes himself as a player. He toured Argentina with the Wallabies in 1987, before being approached by then-Balmain Tigers coach Warren Ryan to switch to league.

The approach convinced him to cross codes, but it was with his hometown Canberra Raiders.

"I always had a handshake deal with [then Raiders chief executive] John McIntyre that if I was ever approached about going back to rugby league I'd talk to Canberra as well, which has turned out to be the right decision," he said.