Verbeek is concerned that the ease of the win may have given Australia a false impression of the standards of Middle Eastern football.
Days after dismissing the Omanis, Australia suffered a 1-0 loss against Jordan in the opening Group B game in Al Ain.
Defeat against Syria on Tuesday in the final group stage match could spell the end for the defending champions.
“Maybe Australia underestimated Jordan a little especially after beating my team 5-0,” Verbeek, who led Australia from 2007 to 2010, told The World Game in Abu Dhabi.
“I don’t think my team helped Australia. I am very sorry about that.
“I was not surprised about Jordan,” added the former South Korea boss who took charge of Oman in 2016. “We play them in the Middle East. They have a Belgian coach and were well-prepared and they can defend very well especially if they score first.”
The friendly meeting may not have been useful for Australia but was worthwhile for Oman.
“Australia were so good and we were so bad. I was disappointed with my team because we had a very good 2018, I think with three goals against in 14 matches.
"After 25 minutes we were losing 3-0. We made individual and organisational mistakes. Organisational mistakes we never make so I was surprised about that. Individual mistakes, there is not much you can do.
"On the other hand, it told me that I can’t use some players in the big games. It helped us, if not Australia. We can learn. If you lose then you learn --which is a quote from my friend Arnie by the way.”
At least Australia recovered to defeat Palestine 3-0 in the second game. “They came back well and scored two goals in the first 20 minutes. The pressure is always there when you are defending champions.
"I still think Australia are one of the top teams in Asia.
“I saw the games they played before against South Korea and Lebanon in friendly matches. If you look overall, they have a strong squad and a good team.
"I was impressed with [Martin] Boyle and it is unlucky that the guy who was scoring goals is injured. You need goalscorers like that and the injuries to [Aaron] Mooy and [Daniel] Arzani were unlucky too.
"They have a good balance with central defenders and midfielders who do well. They have good wingers.
"Physically, they are strong and I think they are good enough to be at least in the semi-finals.”
Oman lost 1-0 to Japan on Sunday thanks to a disputed penalty decision and Verbeek believes that the Samurai Blue offer a different challenge to Australia.
“Japan have a different style of play, keep the ball on the ground and have a good squad, but I think Australia are better defensively than Japan who are an attacking team and take a lot of risks. To score against Australia is not easy.”
That is what Syria have to do on Tuesday. Syria arrived in the UAE tipped to do well but one point from the first two games resulted in the dismissal of coach Bernd Stange, formerly of Perth Glory, and the hiring of Fajr Ibrahim. A win will send West Asians into the knockout stage.
“I am surprised about Syria,” added Verbeek. “I was surprised in the first two games. We saw them play recently and they were tough, physically strong and well-organised.
"Before it started, I expected Australia to finish first with Syria number two and Jordan as a dark horse but now it has changed.”
