Just 19, Clarke will make his NRL debut when the Storm host Parramatta at AAMI Park on Thursday night when the competition kicks off in Australia after two early round-one matches in Las Vegas.
Clarke has been included on the bench which includes another likely debutant in Preston Conn, who was captain of the Storm's Jersey Flegg premiership-winning team last season.
A NSW U19s representative whose father Leo played for Wests Magpies, Clarke has been tagged by the Storm as the long-term replacement for Nelson Asofa-Solomona, who quit the club to pursue boxing.
Coach Craig Bellamy said he'd been impressed by Clarke, who shed weight to improve his mobility and endurance to give himself a chance of a call-up.
"Cooper is only a young kid who will be making his debut - he has done well in the trials, he can play a little bit on the edge and can play through the middle, so he gives us a little bit of versatility there," Bellamy said of Clarke, who played his junior league at Eaglevale St Andrews in south-west Sydney.
"He is a kid that has worked hard for it as well.
"Just presenting his jumper, it was mentioned that when he first came into the under 19s he was 145kg - that is a big boy, so he has certainly worked hard to get down to the weight he is now and to be playing good footy."
Among the other changes as the Storm bid to maintain their remarkable 23-year unbeaten round-one record, former NZ sevens representative Moses Leo will line up for his third NRL match.
Named in the centres against the Eels, 28-year-old Leo signed with the Storm after representing his country at the 2024 Paris Olympics.
He played two matches early in 2025 before injury and stiff competition for spots impacted his NRL chances, but he will replace Nick Meaney who shifts wide to cover injured winger Xavier Coates.
"He has been unlucky with injuries - nothing overly serious - but just seems to be one of those bodies that just needs something small to happen and something goes wrong," Bellamy said of Leo.
"But he's got through this pre-season pretty good, so I think his body's starting to get used to the workload.
"He's got great speed and obviously, learning the defensive system is a little bit different to what he's used to with playing in union.
"That's taken a little while for him, but like I say he's a really good athlete and hopefully he'll fit in tomorrow night."
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