Vietnam Football Federation's (VFF) request to borrow the player was declined as SC Heerenveen expects Hau to participate in the 2nd half of Eredivisie, Holland's highest echelon of professional football.
AFC U23 Championship is not included in the FIFA Calendar, which allows SC Heerenveen the right not to release players.
Hau needs more time to practice and meet the team's strategic requirements to compete for a position in Heerenveen's first team, a representative said.
If Hau were to temporarily return to Vietnam, he might well miss the Dutch season.
VFF and coach Park Hang-seo both respect the Dutch team's decision.
Heerenveen previously released Hau for Vietnam's SEA Games 30 campaign – a tournament also not on the FIFA Calendar, and in which the defender scored two goals in the final, securing Vietnam's first ever gold in SEA Games men's football.
Hau joined Heerenveen in September on a one-year loan from Hanoi FC.
He debuted for the club on December 17, playing the last four minutes in its win against Roda JC.
Heerenveen coach Johnny Jansen promised to grant Hau more game time after the winter break.
The national U23 team will compete in the 2020 AFC Championship in Thailand from January 8 to 26 in Group D, against North Korea, Jordan and UAE.
Vietnam were 2018 runners-up after losing 1-2 to U23 Uzbekistan in extra time. The blizzard-hit match recorded the most iconic goal in AFC U23 Championship history, with Vietnamese midfielder Nguyen Quang Hai's "rainbow in the snow" free kick.