The coach who gave Keith Titmuss his greatest rugby league moment has paid tribute to the unassuming youngster who was destined for the NRL at Manly.

Rugby league is in mourning with Titmuss’ death after a Sea Eagles training session on Monday shocking players across several Sydney clubs.

Titmuss had attended renowned rugby league nursery Westfield Sports, and the 20-year-old had several close friends across the grades at numerous clubs.

The Sea Eagles are continuing to work with police and awaiting the results of an autopsy for the coroner.

Titmuss fell ill after a regulation training session at the club’s Narrabeen base, after noting body cramps.

He was taken to hospital in an ambulance but later died at Royal North Shore Hospital.

It came just three days into his time as a member of the club’s top-30 NRL squad, having made his name as a 17-year-old in the under-20s.

There he scored the match-winning try for Wayne Lambkin’s Sea Eagles side in the last Holden Cup grand final, before being named players’ player in the 2019 Jersey Flegg Cup team.

“He was powerful, just his strength of his running and his after-contact metres were great,” Lambkin told AAP.

“I had him coming off the bench even though he was young, he was capable of doing that.

“To get into the top 30 and a chance of debuting. I know the club had big aspirations for him.

“I have no doubt he would have achieved that least. It’s very sad.”

Lambkin himself had to tell his current Wests Tigers under-20s team of the news on Monday night, many of whom went to school with Titmuss.

Manly’s youngsters who had returned to pre-season training last Thursday, were given Tuesday off, as the club offered assistance to all of their players.

Highlights reels posted by Keith’s brother Jesse emerged on Tuesday, with the front-rower busting through tacklers in both the under-20s and reserve grade.

In a Facebook post, Jesse labelled him his “rock, best friend” and “hardest-working individual” he knew.

“We were just talking about it a couple of days ago about how well prepared he was physically and mentally for pre-season,” Jesse posted.

“All of us as a family were optimistic that Keith was to make his NRL debut in 2021.

“Keith’s memories and legacy will live on forever.”

In rugby league circles, Lambkin knew the front-rower best.

He also coached him at Westfields and watched him come right through the system.

“He was very unassuming, very quiet,” Lambkin said.

“You would say something to him and he would just give you a wry smile or wink and you knew everything was alright. A man of few words.

“We would just yell out ‘Keithy’, and he would give you a smile and wave and we moved on.

“That’s the way he played footy. He knew what his job was and he did it. That was part of the routine.”