After 270 top grade games in both Australia and England in a career spanning 14 seasons, the 34-year-old playmaker ended it all on Monday after letting O'Brien know of his decision to hang up the boots.

It's understood he came to the realisation over the weekend following the Knights' loss to the Cowboys in Townsville.

O'Brien, who has known Green since their Melbourne days together, admitted it was an emotional meeting between the pair.

"As a coach, it's tough to see one of your players retire before they are mentally ready to," he said. "I went though it with Tim Glasby last year and now Greeny. It's a part of the job that is really tough.

"With Greeny, he still sees the game really clearly but with his age and his body, he felt he couldn't contribute the way he wanted too.

"That's the mark of a good leader and a good man that he was able to put the team and the club above himself. That shows a ton of character and courage and it's a selfless human being that can do that.

"I've know him a long time now and he has always been a team-first guy. That's what I love about him. When I think back, he chose us last year to stay and help and wanted to be a part of the Knights and the community. Then he chose us again yesterday with his decision.

"Like I said, he is a remarkable human being. Unfortunately, not everyone gets the fairytale and goes out the way they wanted to."

O'Brien said injuries to key players like Mitchell Pearce and Kalyn Ponga had not helped Green's cause after he fought so hard to get back on the field after a knee reconstruction late last year.

"I really feel for him because I thought had our spine been there, he'd have contributed a whole lot," he said. "But it's a big ask for a guy coming off a significant injury when you don't have the support there and you are the focal point.

"The tragedy is he worked extremely hard to get back and he even got back early than expected."

Green, who played with seven NRL clubs, said it was a tough decision.

"I'm always honest with myself, my teammates and our staff. It hurt, but once I knew retirement was the right call, I owed it to everyone to do it as quickly as possible for the betterment of our football club," he said.

Meanwhile, O'Brien has named injured stars Kalyn Ponga and Bradman Best in his starting side for Sunday's clash against Manly. Kurt Mann has shifted back to five-eighth after Ponga's return after playing fullback against the Cowboys.

English teenagers Bailey Hodgson and Dom Young will return from injury in NSW Cup with Hodgson playing his first game for the club while forward Jirah Momoisea will play his first game for the season after recovering from a ruptured Achilles.

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