Fitzgibbon played only 10 games last year and spent more time in hospitals and physiotherapy rooms than he did on the field.

At the end of 2020, he underwent pelvic mesh surgery in the off-season, only to then need a shoulder reconstruction months later that sidelined him until round nine.

He subsequently aggravated the latter injury in a 28-20 win against Brisbane in August and required a season-ending operation to repair cartilage damage.

More than four months on, the 28-year-old has been training strongly and looks intent on making up for lost time.

"Lachy has already been involved in a fair bit of training," O'Brien told the Newcastle Herald.

"I think the key has been having an uninterrupted pre-season and getting himself right for the season ahead.

"The last couple of years, he's had his setbacks.

"So his No.1 priority right now is just getting himself physically right."

The Knights have spent the off-season exploring the NRL market-place for a line-breaking back-rower, at one stage being linked to promising North Queensland rookie Heilum Luki.

But they are yet to land a notable signing.

Fitzgibbon, who has scored 27 tries in his 89-game NRL career, is a proven strike weapon when at his peak.

"There's absolutely no reason why Lachy can't fill that void for us there," O'Brien said.

"You look at Lachy's best football, it's been of a really high standard and something we need from him.

"It's important that we get him physically and mentally up for the challenge of grabbing that spot.

"But there's no doubt he's more than capable of that."

Fitzgibbon, who re-signed with his home-town team for two seasons in September, faces a battle to dislodge Test forward Tyson Frizell or enforcer Mitch Barnett from Newcastle's starting pack.

Cessnock junior Brodie Jones also made great progress last season to appear in 22 top-grade games.

But Fitzgibbon's ability to slice through defences could potentially increase the Knights' firepower after a 2021 campaign in which they scored only 428 points, the second-fewest in the competition.

Barnett is also equally at home playing lock, which he might be required to do during the early rounds while Sauaso Sue is sidelined.

Sue, who played in 23 games last year after joining the Knights from Canterbury, has had two bouts of shoulder surgery over the off-season and will miss the opening rounds of 2022.

O'Brien said Sue was "tracking well", as was Jack Johns, who also needed a shoulder operation.

"They both had some issues coming out of their surgeries," O'Brien said.

"I don't have a definitive timeline on when they will return, but I'd imagine it'll be the early part of the season."