Prominent NRL coach Des Hasler has told the family of late Manly Sea Eagles player Keith Titmuss he's "so, so sorry".

Experts told an inquest earlier this week, the 20-year-old died of exertional heat stroke after a pre-season training session overseen by Mr Hasler in November 2020.

"I'm so, so sorry, I share your heartbreak, I really do."

The inquest heard Mr Titmuss scored lowest in the team on a pre-season fitness test.

Other players testifying earlier this week have told the inquest it was a "hard" session and ranked it nine out of 10 in terms of intensity.

Mr Hasler was asked if he felt that, given the state of Mr Titmuss's fitness, the session would have been demanding.

"Parts of it would have been challenging … but there were also planned stoppages to give players the opportunity to recover and to rehydrate before we move to the next phase," he said.

He said he would have rated the intensity of the session as six or seven out of 10.

"We wanted to make sure it wasn't too arduous. We don't want to place the players in a position where they can become injured."

Mr Hasler told the inquest there was an inherent tension between players wanting to push themselves and impress coaches, and coaches wanting to restrain them to avoid injury.

Counsel assisting coroner Adam Casselden asked Mr Hasler if he would do anything differently in hindsight.

"I don't know if there would be parts there that I could change."

The council assisting also highlighted an email from a former club medical officer, Luke Inman, to the ex-head of sports science, Mark Booth, warning about heat monitoring at training in 2019.

"You are leaving yourself open to litigation from a player if they suffer heat stress or at worst, dies," the email warned.

Earlier in the day, the inquest heard from former Sea Eagles Club medical officer Nathan Gibbs.

He recommended the NRL mandate a staggered approach to pre-season training to reduce the risk of exertional heat stroke.

The inquest will continue next week.