Klemmer was a late starter to pre-season training after playing in Australia's Test campaign, which ended with a 16-12 loss to Tonga on November 2.

The prop, starting his third week of training at Newcastle, said on Monday that pre-season under O'Brien had been "pretty tough".

"Obviously Browny had his own style and Adz has got his own style as well," Klemmer said of the differences in pre-season under former coach Nathan Brown and O'Brien.

"They are both good coaches and obviously Adz has come here and brought expectation on him.

"He's been pretty hard on us since I've come back and the boys said he'd been pretty hard on them since they've come back.

"It's a new challenge for us and obviously Adzy brings his own style and what he wants from us and the club as well, so it's exciting times.

"Adzy has been at Melbourne and the Roosters the last couple of years and he has a lot of experience, and in what it takes to be a good footy side.

"Obviously he has brought it here and it's just sort of a shock for everyone, the intensity that he brings, it's good. It's good for us as a playing group."

Klemmer was not afraid to show his frustration on the field last season as the Knights faded from finals calculations to finish 11th.

The pack leader was optimistic about Newcastle turning it around next year and believed the memories of 2019 would fuel change.

"Obviously getting flogged, on the back of those scores, it's pretty disappointing to be a part of and it was frustrating," he said.

"But coming in here, there's a new attitude around the club now I think.

"And where we want to be in the future, we don't want to be one of those sides again.

"It's pretty shit being there, on the bus home. It's a long trip after getting flogged, so the boys have got it in the memory bank and they don't want to be there again."

O'Brien has flagged the importance of strong defence in his tenure at Newcastle, and Klemmer welcomed the focus.

"Last year we leaked a few points, and Adzy has been at sides where defence wins footy games and defence wins comps," he said.

"He's been pretty hard on us in our D, especially out on the footy park under fatigue and when we're hurting, we've still got to turn up and defend.

"It's just something we definitely have to improve on from last year because it was pretty disgraceful. At the back end of the year, it was pretty bad."

Klemmer opted against surgery on his wrist, which was fractured in Origin I in June, to be the Knights' only representative in the Kangaroos. He said his body was "a bit wrecked" after the Tests, but he expected to avoid an operation on his wrist.

"The wrist feels good at the moment, and it's getting stronger," he said. "I've just got to look after it."

Klemmer will take part in NSW Origin preparation camp on Thursday and Friday at the NSWRL Centre of Excellence in Sydney.