Numerous boys reportedly do not know how to swim and do not have experience using scuba equipment.
The navy is also seeking permission to posthumously promote Saman, who was a petty officer first class when he left the unit, Channel News Asia reports.
It is noted that the 38-year-old officer in the Thai Navy lost consciousness, when delivered oxygen tanks to children.
His diving partner tried performing CPR on him but was unable to revive him.
"It was sad news".
"A former SEAL who volunteered to help died at around 2 a.m.", Chiang Rai Deputy Governor Passakorn Boonyaluck told reporters at the rescue site. "His job was to deliver oxygen. We have a limited amount of time", he said.
Many fans on social media said the boys deserved the World Cup trophy for the way they have handled their ordeal.
"We have been trained to always be dealing with risks", he said. "We will not let our fallen brother die in vain".
The elite diver's death underscores the difficulty and complexity of attempting to rescue the 12 boys, ages 11-16, and their 25-year-old coach. The boys are said to be too weak from malnutrition to even make the trek.More news: Flawless Federer sweeps past Lacko; Wozniacki falls in three sets
"We are awed by the bravery and strength that these young boys and their coach have shown amidst such frightening circumstances", it said on its website.
Numerous boys - aged between 11 to 16 - are unable to swim and none has scuba experience, further imperiling any attempt to dive out of the cave.
If the weather is on their side and enough water can be pumped out of the cave, the boys could get out the same way they got in, on foot, perhaps with some swimming.
The president of soccer's governing body, FIFA, invited the boys on Thursday to be his guests at the World Cup Final in Moscow on July 15 if they make it out in time.
A team of Royal Thai Navy members, a doctor and a nurse have been staying with the group ever since, giving them high-powered protein drinks and medical assessments, while officials work on a plan to get them out as safely and quickly as possible.
The Navy source said boys' biggest challenge would be a 200m stretch of the completely flooded cave that made up part of the 600m section between "Pattaya Beach" and chamber three.
Rescue teams have been pumping millions of liters of water from the cave in an attempt to lower water levels to the extent that the boys can simply walk out. "We will complete the mission for you".
Messages of support for the "Wild Boars" team have come in from across the world, including from football stars in Russian Federation for the World Cup.
Rescue teams, meanwhile, have thrashed through dense forest above the cave complex, looking for a place to start drilling a rescue shaft.
The diver's mission was to bring oxygen tanks and carry lines along the passageways between a forward operating base and the muddy embankment where the children and coach are sheltering.