Keith Titmuss suffered a seizure after a cardio workout at the club's base in Narrabeen, on Sydney's northern beaches, on November 23, 2020.
The 20-year-old was transported to Royal North Shore Hospital, but died five hours later having suffered a cardiac arrest.
An inquest in February was told Titmuss most likely suffered exertion heat stroke, although an autopsy was unable to confirm the exact cause.
Specialist acute-care physician Simon Quilty told the inquiry sporting codes should enforce a standard two-week acclimatisation period when players return from the off-season.
It was well-known there is a high risk of exertion heat stroke and heat illness in the first five days after players restart training, he said.
"That extends out to 14 days, so it makes sense that a 14-day period of acclimatisation should be a standard across all sporting codes, not just professional sporting codes," Mr Quilty said.
Veteran rugby league coach Des Hasler, who is now head coach of the Gold Coast Titans after his 2022 sacking from the Sea Eagles, expressed his condolences to Titmuss' family.
"I am so, so sorry and I share your heartbreak, I really do," Hasler said.
Hasler said there were no "red flags" raised with him about Titmuss' physical fitness, adding the session was challenging, but included rest breaks for players to recover and rehydrate.
"It was the first training session back with the new group so we were very cautious of not overloading," he said.
"From the outset, particularly for younger players, there is a need not to overstride ... to overcome that emotion of, 'I must succeed, I must impress the coach'."
Titmuss' mother Lafo said earlier she is grateful for the inquest providing clarity and understanding regarding the events that led to her son's death.
"Keithy loved Manly, he loved his brothers in arms on and off the field, and he loved and respected the training staff," she said.
"We sincerely hope the recommendations from this inquest will be instructive, not just to the NRL, but all codes across Australia and worldwide."
Deputy State Coroner Joan Baptie is set to deliver her findings on Friday.
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