Captain Chan Wai-ho said Hong Kong had made little progress in the past decade while other countries in the region have improved significantly.
Just 10 days before the two sides meet in a 2015 Asian Cup qualifier, Chan admitted Hong Kong would be the underdogs against Vietnam at Mong Kok Stadium on March 22.
"I was really surprised when we played them in a friendly last year," the centre-half said after training yesterday. "In terms of individual players' skills and team tactics, they are superior.
"That was hardly the case when I played against them 10 years ago in the Olympic qualifying tournament. They were a modest side then but somehow they have made huge progress over these years."
Vietnam won last year's friendly 2-1 at Mong Kok Stadium. Vietnam are now ranked 134th in the world compared with Hong Kong's ranking of 156.
"I don't know why there is such a big gap between the two sides. But what I do know is that we have produced very few quality young players in recent years, while Vietnam must have conducted a very successful youth training programme. Otherwise, they wouldn't have so many good players coming through the ranks," he said.
"But if Vietnam can do it, we must ask ourselves why we can't. People in the soccer fraternity should reflect deeply."
The South China skipper said the only youth player who had met international standards recently was his club and national team colleague Yapp Hung-fai - the goalkeeper.
And the team can rely on the 22-year-old Yapp to keep it tight at the back, allowing Hong Kong to go on the counter-attack.
"The best way to tackle Vietnam is probably to stay tight in defence and wait for the opportunity to attack," said Chan. "We are very strong in defence as you can tell from our last match against Uzbekistan when we held them to a goalless draw. Now we also have some very speedy players up front such as Lee Wai-lim and his brother Lee Hong-lim and Jaimes McKee, and they are all very useful for this kind of team tactic."
Meanwhile, coach Kim Pan-gon said he would select his final team from the current 29-strong training squad on Friday, but is waiting for more information on forward Godfred Karikari, who plays for Chinese First Division side Henan.
"Karikari has not been training due to injury since the close of the Chinese season in November," said Kim.
"I am a bit worried about his form and if he can't rejoin club training this week, I have serious doubts he will be ready for the Vietnam match."
Kim, however, is confident that another mainland-based player, Chan Siu-ki, will be available. "We know he has been in very good form and his inclusion can give us more attacking options," Kim said.