Spurs centre-back Micky van de Ven has revealed he "was completely surprised by" the club's move to part ways with former manager Postecoglou.
Postecoglou's spell in charge came to an end a just over two weeks after he guided Tottenham to a win in the Europa League final, securing the club's first major trophy in 17 years.
However, this European success was not mirrored in the domestic league, with the team finishing in a disappointing 17th position in his last season in charge.
He was succeeded by ex-Brentford manager Frank during the off-season, but Spurs are presently 11th in the table, with 22 points from 16 games, following a 3-0 defeat to Forest at the weekend.
"He was a really good manager. I still really like him," the Dutch defender stated on a podcast.
"I don't know how everything went backstage. I didn't expect it. It was strange how everything went afterwards - he is the coach that won silverware to Tottenham," he continued.
"Afterwards, when he was dismissed, I sent a message to my father and my mates and said, 'I never expected this.'"
Postecoglou joined Tottenham from Scottish champions Celtic before the 2023-24 season, replacing Antonio Conte. He enjoyed early success with his attacking style of play, collecting 26 points from his opening 10 Premier League games.
Nevertheless, that fine start came to an abrupt end with four defeats in five games, and the club's season tailed off, eventually failing to secure Champions League qualification by a mere two points.
In the next campaign, they managed only 11 of their 38 league matches.
While he appreciated Postecoglou's style, Dutch international the defender believes the team lacked a "plan B" and revealed he and defensive partner Romero discussed taking a more defensive approach with the manager.
"I liked the attacking football at that time but I like what we have now with Thomas Frank. We are more secure defensively. I don't like being vulnerable every game on the counter-attack," he said.
"At the beginning under Postecoglou, no team was used to playing against our style. We were playing unbelievable football."
"But, managers study everything and people figured out what we were doing. Sometimes we lacked a backup plan and we were being caught out. We didn't have answers to resolve it."
"At one point me and Romero approached the gaffer and suggested we should adjust tactically and be more defensive to make sure we win those games. He was responded, 'I agree with you but I want you two guys to handle this on the pitch, ensure everybody knows.'"