The 19-year-old forward has been thrust into action since arriving on loan from Bayern Munich, with a permanent move expected in the summer.
However, Postecoglou urged patience, stressing that Tel is still building sharpness after limited game time in Germany.
“I don’t think he’s going to be that kind of striker but that doesn’t mean he can’t be a really good central striker, there are different types,” Postecoglou said.
“With Mathys, he hadn’t played a lot, we’ve thrown him in and kept him in there because I want to build up his fitness.
“But if anyone is expecting him to come in as a 19-year-old and take the Premier League by storm by scoring multiple goals, it’s not realistic. It just can’t happen.
"What we’re trying to do is work with him. He needs to get his physical fitness up because he hasn’t played a lot of football.
“At 19, I see really outstanding attributes in him that I think he could be a really good No9 and he can play wide as well. He’s not going to be a Dom or (Ipswich’s Liam) Delap, he’s a different type.
“But looking at him in training, his movements are becoming a bit more fluent, he’s getting used to the way we play.”