Many Sea Eagles player Keith Titmuss suffered a seizure after a cardio workout at the club's base at Narrabeen, on Sydney's northern beaches, on November 23, 2020.
He died five hours later in hospital.
An inquest into the 20-year-old's death previously heard he most likely suffered exertional heat stroke, although an autopsy was unable to confirm the exact cause.
The inquest previously heard Keith Titmuss most likely suffered exertional heat stroke. (HANDOUT/MANLY WARRINGAH SEA EAGLES)
Hasler, now head coach of the Gold Coast Titans after his 2022 sacking from the Sea Eagles, said young players in particular were eager to prove themselves.
But it was up to the club to create a culture that made it acceptable not to overexert themselves and cause an injury.
"It's really important once (players) come under our duty that there is a real focus on knowledge absorption and understanding about their journey," he said.
"It's really important from the outset, particularly for younger players, that there is a need not to overstride ... to overcome that emotion of, 'I must succeed, I must impress the coach'."
Asked if he would have conducted the training session differently, knowing what he does now about heat exertion, Hasler said it was a difficult question to answer in hindsight.
"Anyone that is under my care, I would do anything to prevent such a tragic accident," he said.
"Before the training sessions start we instruct the players and show them the plan of what is to happen and if they're feeling ill or feeling like they're not coping well with it ... that they raise their hand and let us know.
"It's essential (for them) to understand the last thing we want to do is to injure them or not to have them on the field, that's really important as part of our culture."
As one of the first sessions back following the off-season break, Hasler said it would have been challenging.
"But there were also planned stoppages so that players had the opportunity to recover and rehydrate before we moved to the next phase," he said.