Sint-Truidense temporary coach Nicky Hayen said: "Jupiler Pro League is underestimated by many. Playing football here requires every player to be very active on the field, even when they lose possession.
"It means that attackers also have to take part in the defensive duties. But Cong Phuong is not familiar with this. He only thinks about offense and doesn't care about defense. It's 2019 now and that is not suitable with football in Belgium," Hayen told the Het Belang van Limburg.
However, he also said Cong Phuong was not to blame.
He said Phuong is a polite and friendly player who always tries his best in the training.
"But he is not suitable with the 5-4-1 formation that I'm using. I’m not saying that Cong Phuong will never be adaptable, but I guess we'll never know."
David Meekers, president of the Sint-Truidense club that hired Cong Phuong, said they regretted his departure.
"This is a disappointment for Cong Phuong. In his country, he's like Eden Hazard to the Belgian. His departure is a matter of regret for us," Meekers said, as cited in the report.
He also admitted that Cong Phuong's deal had a commercial slant to it.
He said Phuong is a player with great marketing value and if he had succeeded with Sint-Truidense, the club's owner could have opened the doors to the Vietnamese market.
Phuong, 24, has been a key player at Vietnam's major regional events in recent years.
He joined Sint-Truidense on loan from Hoang Anh Gia Lai FC in July. But he did not have many chances to prove himself, and when he did, he was not able to make much of an impression.
Under the previous coach, Marc Brys, Phuong only played 20 minutes in the match Sint-Truidense lost to Club Brugge on August 3.
After that, Phuong had to stay on the bench for game after game and sometimes he was not even registered in the squad list. Phuong also failed to impress when he played for the U21 team of Sint-Truidense.
HCMC FC came to his rescue last week, deciding to buy the remaining half of the one-year loan deal signed between HAGL FC and Sint Truidense in July. Cong Phuong will sign the new contract as soon as the transfer window opens on January 1.
HCMC FC chairman Nguyen Huu Thang is hopeful with the deal.
"Cong Phuong is a very good player. I am sure that he will be able to demonstrate his full capabilities at HCMC FC," Thang told local media. His club now ranks second in V-League.