Dan Lydiate has highlighted the threat of Ireland flanker Sean O'Brien to Wales' World Cup semi-final hopes.
Lydiate and his Wales back-row colleagues Sam Warburton and Toby Faletau face arguably their biggest test as a unit in tomorrow's quarter-final showdown.
And Lydiate, back in World Cup action after missing Wales' last two games through injury, expects a fierce examination from Ireland.
"He (O'Brien) is a class player," Lydiate said. "He was European player of the year last season.
"And it isn't only him. Stephen Ferris was on the (2009) Lions tour and Jamie Heaslip is a Lions Test player, so they have arguably the best back-row in the tournament.
"O'Brien is a go-to man, someone who always gets them over the gain-line whoever they are up against.
"It does take a lot of people to stop him when he has those bullocking runs. It's our job to try to nullify him.
"We must not miss any tackles and, as best we can, keep knocking them back. Playing against South Africa and the Pacific islands teams has put us in good stead.
"They are all big blokes, so the boys are conditioned to deal with powerful men who take some stopping."
Victory for Wales would see them book a first World Cup semi-final place since 1987, while Ireland have never reached the last four.