In the heats Tuesday night, Hoang had finished with a time of 7 minutes and 54.16 seconds, second in his group after New Zealand’s Zac Reid.
However, in the overall result for five groups, he was in 20th place among 34 athletes. Only the top eight can advance to the final round.
The first place in the heats belonged o Ukraine’s Mykhailo Romanchuk with a time of 7 minutes and 41.28 seconds, followed by German’s Florian Wellbrock with 7 minutes and 41.77 seconds.
Hoang’s best result in the 800m freestyle was at the Youth Olympics 2018 when he registered a time of 7 minutes and 50.20 seconds.
The 21-year-old swimmer is participating in the 1500m freestyle event that will take place on the evening of July 30.