Lacuna, one of the 50 swimmers to dispute the eight slots for the next phase, clocked 4:01:70, the second worst in heat 2. His finished 46th overall.
The 23-year-old swimmer from Ateneo de Manila University raced in a heat of seven swimmers.
His personal best in the 400m freestyle is 3:59.75.
Venezuelan Cristian Quintero registered the quickest time in the same heat, but he wound up finishing 33rd in the final ranking.
American Dwyer Conor logged the best time of 3:43.42.
Lacuna, who currently holds the record 2015 SEA Games record of 2:00.9 in the 200m butterfly, is the second casualty the Philippine contingent suffered in the Games.
The Bulacan native also competed in the 2012 Olympics in London, where he ranked 36th in heat 2. He was the youngest athlete in that year's Philippine contingent.
Earlier, Ian Lariba bowed out of contention in the hands of naturalized Congo paddler and frequent training mate, Han Xing in the women's table tennis singles.
The Philippine crew is now down to 11 athletes.
Charly Suarez is next to see action. He will take on Great Britain's Joe Cordina in the men's lightweight boxing which begins Sunday, 5 a.m.
source: philstar.com
