The whole squad, including the support staff, are fully vaccinated, and only he tested positive.
He was quarantined immediately, and his assistant Nguyen Tuan Anh had to lead the team against Russia.
Vietnam still played impressively against world number four Russia.
After conceding two goals, they got one back before Russia scored a third. In the dying minutes, Vietnam narrowed the gap again to finish 2-3.
This is Vietnam’s second time at the Futsal World Cup after first qualifying in 2016.
In the group stage Vietnam were crushed 1-9 by Brazil, but rebounded to beat Panama 3-2 and tie 1-1 with the Czech Republic to advance as one of the best third-placed teams.
After Vietnam exited the tournament, Giang said on Facebook he was in good condition and thanked the fans for supporting the team.
"I hope people will maintain their love for futsal and motivate the team in future."
Futsal World Cup: Vietnam 2-3 Russia