Saracens and England hooker Jamie George knows all about how important the set-piece will be against Munster in the Champions Cup semi-final on Saturday (KO 3.15, BT Sport 2).
He got a close-up look at what Peter O'Mahony can do to the best organised lineouts in the game on the 2017 Lions tour to New Zealand.
It was there George beat off Rory Best and Ken Owens to be the test starter with O'Mahony nominated to lead the Lions in the first test before dropping out for tests two and three.
"Look, first of all, I think 'what an incredible man,' an unbelievable leader," said George.
"In terms of captaincy, on and off the field, he was one of the best I've worked with, even if it was for a short period of time.
"His record speaks for itself, how many Ireland caps, British & Irish Lions captain.
"He's got an aur a about him, an incredibly impressive character."
Munster will make a plan for O'Mahony's athleticism and sixth-sense at the lineout to climb inside George's head.
"I think he is one of the best lineout defensive players in the world and I saw that first-hand on the Lions tour.
"It's going to be difficult. It's so important for the chain of command to work well.
"There's pressure on myself to get the ball to where it needs to be.
"It's a big area of the game and the set-piece will go a long way to defining the game."
While O'Mahony tops the lineout steals in Europe, Tadhg Beirne heads the turnover table.
"We are certainly aware of the threat that he brings," said George.
"He is very strong over the ball. We have a plan in place to try to take that away from him.
"In big European games, there's always a huge emphasis on the breakdown.
"That is an area where they pride themselves and an area we have to make sure we're right on it to keep our attack flowing."