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."
Verbeek named an expanded 31-man squad to cover for injury doubts clouding a number of players. The squad will be trimmed to 23 ahead of the June 11-July 11 finals.
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.
In a squad largely comprising the Europe-based core that guided Australia to a surprise appearance in the knock-out rounds at Germany in 2006, Verbeek sprung few other surprises but handed a life-line to Middlesbrough striker Scott McDonald.
McDonald, who despite prolific goal-scoring at club level in the Scottish top-flight, failed to net once in 15 appearances for the Socceroos.
"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.
The Dutchman also played down fitness concerns over Kewell, who will be expected to shoulder some of the scoring duties with Everton midfielder Tim Cahill and Nagoya striker Josh Kennedy.
Kewell has struggled to recover from a groin injury that has kept him out of Turkish club Galatasaray this season for all but a few minutes.
"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."
Australia play their first World Cup match against Germany on June 13, and also play Serbia and Ghana in Group D.
Goalkeepers - Mark Schwarzer (Fulham), Adam Federici (Reading), Brad Jones (Middlesbrough), Eugene Galekovic (Adelaide United)
Defenders - Lucas Neill (Galatasaray), Craig Moore (unattached), Scott Chipperfield (Basel), David Carney (Twente Enschede), Luke Wilkshire (Dynamo Moscow), Rhys Williams (Middlesbrough), Shane Lowry (Aston Villa), Mark Milligan (JEF United), Jade North (Tromso), Michael Beauchamp (Al-Jazira)
Midfielders -
