The midfielder suffered an ankle injury during Vietnam's 1-0 win over Thailand on Tuesday at the Go Dau Stadium.
The national U23 player went down early in the second half and looks set to miss the final.
"He won't make it to the final. We have several substitutes who can play as attacking midfielders like Truong, but his absence will partly reduce our power," Coach Dinh The Nam said.
"But I believe that my team will win."
Vietnam advanced to the final thanks to an early winner by Nguyen Dinh Bac in the 14th minute.
The win pushed the hosts to the top of the four-sided competition with three wins.
"I made four changes in this key match against arch-rivals Thailand. We played well in the first half and scored a goal. The second half belonged to the Thais but we kept them out," said Nam.
"My players showed strong minds and good spirit the whole match. They also created threatening chances. These were good signs. But some players were not strong enough for the whole match. It was a problem.
"Anyway, I am happy with every victory and look forward to more."
Nam and his players were awarded VND300 million (US$12,800) for the win.
On the Thai side, coach Salvador Garcia was not disappointed even though this was the fourth time his team lost to Vietnam in all competitions.
"We were met with tons of problems in the first half. I made some changes which led to a better second half. My players created opportunities but they could not score," Garcia said.
The Spaniard said he considers Vietnam a good opponent. They are not the enemy so the Thai players were not asked to beat them at all costs. However, they were encouraged to try their best to win.
The tactician said the loss provided good lessons and he found weaknesses that must be fixed ahead of the 2023 AFC U19 Championship's qualification.
In the other match, Malaysia beat Myanmar 2-0 to place second, setting a date with Vietnam in the final which will be live from 6pm on VTV6, FPT TV, FPT Play and other internet platforms.
In their first meeting in group-round on Sunday, Vietnam came from behind to beat Malaysia 2-1.
Meanwhile, Thailand will clash with Myanmar for the third-place position. Thailand won 1-0 in the group round meet.
Speaking about the final, Garcia said it would be an attractive match between two teams who are equal in both technique and fitness. The tactics of the coaches may decide the game.
Source: Vietnam News