The 18-year-old Oar, who has been dubbed Australia's "next Harry Kewell" by enthusiastic local media for his feats in Australia's domestic league, has played only one international, against Indonesia in an Asian Cup qualifier in March.
"Very, very promising (player)," Dutchman Verbeek told reporters on Tuesday of Oar, who has signed with Utrecht in the Netherlands' top flight after impressing at Brisbane Roar.
"I think it's great for Australian football that we have a player like him, just 18 years old. (He) made a big impression in the few weeks in the Netherlands.
"I'm sure Tommy can be a great player in the future, so it was good for him to be part of this selection especially (since) you don't have so many left-footed players with his qualities.
"But still he has to show that he's not only a talent, that he's also a great player."
Oar's fellow Dutch league player James Holland, who will celebrate his 21st birthday on Saturday, was also a surprise call-up.
"I saw him more than several times in his club at AZ Alkmaar. Central midfield at the moment, we all know him as an attacking midfielder," Verbeek said.
"So far he didn't (score) in the national team, but it's time for him now to score some goals so hopefully he waited to do that job (for) the World Cup," Verbeek added.
"Of course there are rumours, of course there are opinions, but he will be ready," Verbeek said. "We still have five weeks to prepare him for the game against Germany."
