Tonga have some of the "best open field runners" in rugby and will be a "real challenge" in Saturday's Rugby World Cup Pool B match, Ireland defence coach Simon Easterby said.
He warned the Tongans would be "a big step up" for Ireland from a Romania side that the Irish outclassed to post an 82-8 thrashing last Saturday in Bordeaux.
Tonga will be playing their first match of the tournament but the squad's quality has been boosted by the inclusion of several former New Zealand stars with Tongan heritage.
Among them are fullback Charles Piutau and centre Malakai Fekitoa, the latter a member of the All Blacks squad that won the 2015 World Cup.
"Tonga have some of the best open field runners in World Rugby," said Easterby at Friday's press conference in Nantes.
"They have players in the forward pack who can mix it and offload.
"Their backline has attacking threats they will be a real challenge defensively.
"This will be a big step up from Romania," added the 48-year-old former Ireland backrow forward.
Piutau -- capped 17 times by the All Blacks before he moved abroad after being omitted from the 2015 World Cup squad -- is certainly on his opposite number Hugo Keenan's mind.
"He is a serious player," said Keenan of Piutau.
"He is a real danger and threat for them. He is experienced but they have threats across the backline and we have familiarised ourselves with them this week."
Ireland head coach Andy Farrell, recognising the threat of the Tongans, has picked a strong team including captain Johnny Sexton, Keenan and others who propelled the Irish to the Six Nations Grand Slam last season.
Prop Tadhg Furlong said: "Of course we respect Tonga and the players. You think of where they're coming in from.
"It's their first game of the World Cup, the players play all over the world and it must be special for them to get a bunch of them in a room to gel and bond for a prolonged pre-season.
"We are quite lucky we get to do it the majority of time in Ireland."
The Irish managed to sparkle against Romania despite playing in temperatures of around 36 degrees Celsius (97 degrees Fahrenheit) last Saturday. Prop Andrew Porter lost four kilos (eight pounds) during the game.
Nantes is predicted to be 23 degrees on Saturday when the match kicks off at 1900 GMT.
"I was thinking of putting a jumper on today compared to what we've been used to," said a poker-faced Furlong, sparking laughs.
"It doesn't feel as hot, like an oven, or someone blowing a hairdryer in your face like it has been for the last few weeks."
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