Former England international Jason Robinson says Jarryd Hayne is not guaranteed his place in Fiji's sevens squad after leaving NFL to pursue his Olympic dream.
Hayne left NRL side Parramatta Eels in 2014 to start an NFL career with the San Francisco 49ers and became a cult figure after several sensational plays in the pre-season last year.
However, Hayne was given limited opportunities to impress during the regular season and ended the campaign with only 79 total yards on 23 touches from scrimmage.
Hayne claims Fiji - his father's homeland - "reached out" to him ahead of the Games in Rio, but subsequent reports have suggested his chances of involvement are slim.
The Pacific nation currently lead the World Series standings and Robinson says Hayne will not walk into a successful side.
"I think one of the main things is whether he'll make the team," he told Omnisport at the publication of the HSBC Future of Rugby report. "Fiji have got a fantastic pool of players. They are sitting at the top of the HSBC [World Series] table at the moment, so it's not going to be an easy ride for players coming in from American football, from 15s.
"It's a great opportunity and they know they've got to work hard to get in there because the fitness of NFL and 15s is quite different to the fitness of sevens. I can see that being quite tough for him.
"He's a great athlete, but there's no givens in this game. You have to work exceptionally hard, but what an opportunity for sevens - the fact that he wants to play."
Robinson concedes that simply having Hayne involved is a huge boost for the sport, which is making its Olympic debut this year.
"Jarryd Hayne is a world class athlete," he added. "He's played NRL rugby league, was one of the best players out there before he left to go to the NFL.
"He spent a season in the NFL and all of a sudden he wants to play for Fiji in Rio, and that speaks volumes about how big this event is.
"To go from the NRL to the NFL and then want to play in the sevens is great for the game. The more players that we have - [United States'] Nate Ebner is one that has come from the NFL, Perry Baker [also US] has got an NFL background - it's great that all of these different players, whether it be from NFL, from 15s wanting to go and play sevens, they all want to come and they see the excitement.
"They want a gold medal and I think it can only be good for the game."
The HSBC Future of Rugby report revealed that participation in the sport could reach 15 million by 2026, with women set to be the primary growth driver, representing more than 40 per cent of worldwide rugby union players in a decade's time.