The Knights had the second-worst attack in the competition last year, and Connor Watson's departure was only another issue they had to solve.
Mann played at lock last week in their first trial against the Canterbury Bulldogs, putting in a strong performance.
It has been widely acknowledged that Phoenix Crossland was training as a lock forward, however, Mann appears to have won the race.
Asked if he was confident Mann would start at lock in Round 1, O'Brien replied in the affirmative.
"Yeah, I am. I anticipate that Kurt will start at that 13 position," O'Brien told Fox League ahead of the trial against Melbourne.
"We have trained across the summer with both him and Phoenix sharing that role.
"That utility that can connect up our edges. We have been really vocal in wanting to use the ball a lot more, and I think he provides that for us."
He also revealed just how important Adam Clune has been.
His first appearance against Canterbury last week was strong, and the former Dragon will be looking to stamp his name all over a starting spot in the Knights' team ahead of the likes of Simi Sasagi, and the lock duo of Mann and Crossland.
"He (Adam Clune) has been outstanding," O'Brien added.
"The thing that stood out for me - we had him missing for about four days after Christmas - I felt our sessions really dipped. That's how much we missed him and that's when I knew we had a good player on our hands.
"He has been outstanding. I thought he and Jake did a good job and they'll only evolve the more time they get to spend together.
In a spot of good news for Knights' fans, O'Brien confirmed the Saifiti twins would be okay to play in Round 1 when the Knights take on the Sydney Roosters at the Sydney Cricket Ground.
"Yeah, look, they'll be fine for Round 1," O'Brien said.
"Daniel has a sore foot and Jacob jarred up his back at training.
"With the flight down, they weren't worth the risk. They'll do some training in Newcastle and be right for Round 1."