Angus Crichton admits he is facing a man in "beast mode" in the NRL semi-finals, but insists the Sydney Roosters can find a way to shut down Haumole Olakau'atu.

One week after Olakau'atu busted 11 tackles in a heavyweight showdown with Viliame Kikau, another one looms this week against Crichton and the Roosters.

Olakau'atu was close to Manly's best in their 24-22 elimination-final win over Canterbury, in what has so far been the most damaging year of his career to date.

Crichton played alongside him for NSW this year, while Saturday night will be the first time the pair mark up against each other on the same side of the field.

"He has been playing beast-mode footy the last couple of weeks, and especially (against Bulldogs), he just carved up," Crichton told AAP.

"He's such an integral part of their team. I am keen to mark up against him."

Asked whether it was possible to minimise Olakau'atu's mark on the game, Crichton suggested he felt the Roosters could.

"I'd like to think we can try and limit his impact," Crichton said.

"We know what he is going to bring. Big powerful, strong, fast and physical. And we'd like to think we can do all those things too."

For all of Olakau'atu's threat, Crichton also has the potential to break open Saturday night's semi-final at Allianz Stadium.

Manly's right-edge defence was found wanting against Canterbury on Sunday, and Crichton is a front-runner for Dally M second-rower of the year.

He leads all second-rowers for offloads and try-assists this year, while also scoring 11 himself.

But Olakau'atu said he was ready to rise for the challenge again, thriving on pitting himself up against the likes of Kikau and Crichton.

"Gus (Crichton) has definitely been the best second-rower in the game," Olakau'atu said.

"It just means I have to step up my game.

"I try and challenge myself against the best. It's definitely something I am looking forward to.

"It will be a challenge, but I am ready."

The Sea Eagles second-rower said he had also made a point to learn from Crichton in Origin camp, watching the Wally Lewis Medal winner closely at training.

"Gus is an extraordinary player, and even better bloke off the field," Olakau'atu said.

"Just to observe him, you learn so much.

"Just the way he is and presents himself on and off the field. He doesn't stop, he is just full throttle at training and it shows on game day.

"It's good to go up against him, and I'm ready for the challenge."