Australian halfback Josh Holmes expects last-minute Fiji recruit Jarryd Hayne to excel in this weekend's London Sevens tournament, but he has a stern warning for the former NRL star.
Expect your lungs to burn.
Holmes is a relative newcomer to the sevens format himself, barring one tournament about 10 years ago before his Super Rugby career.
He signed with the Aussie team two months ago and this weekend's tournament at Twickenham is just his third since then.
And Holmes is the first to admit he's still adjusting to the games gruelling physical demands.
"It's probably one of the hardest games professionally out there," Holmes said.
"Every team is just training harder each year, you can see by the calibre of some of the players with the things they can do already.
"The skill sets of some of these guys on the circuit is unbelievable and the level you need to get your body to and your fitness, and your mindset before you go into these tournaments is pretty crazy.
"It's definitely not something you can just walk off the street and walk into."
Which is essentially what Hayne hopes to do this weekend.
The two-time Dally M Medal winner only arrived in London on Monday, barely hours after quitting a lucrative contract with the San Francisco 49ers in the NFL.
The 49ers coach, Chip Kelly, was just as surprised as the international sporting public by Hayne's decision, and has since indicated the Australian was part of his plans for the 2016 NFL season.
Hayne was on Friday named in Fiji's 12-man squad to play this weekend, stepping in for injured playmaker Vatemo Ravouvou.
It means he has potentially six games to prove to Fiji coach Ben Ryan that he is Olympic-worthy.
"I don't think it's a question of his making it. I'm sure his lungs will burn, but he's a pretty talented kind of guy, I don't think he'll be out of place," Holmes said.
"A lot of guys who have dominated the international stage like your Bryan Habanas and Sonny Bills, they've come in and they're outstanding players and they've just mingled in and haven't been the best, although they're pretty close.
"I think it'll take some getting used to with all the players he's got in the Fijian team. In saying that, he's a pretty special athlete with what he can do.
"He'll learn a lot this weekend."