Koeman admits that Calvert-Lewin is far from the finished product, but believes that the highly-rated forward has a big future ahead of him.
"In most aspects of football he needs to improve - in holding the ball and in his movements - but if you look into other strikers of his age then he's really a big talent," Koeman told Sky Sports News.
"He's strong, he's fast and he showed yesterday he can score goals, but he can be more clinical and that's normal - nobody at that age is totally in every aspect good.
"He's really disciplined, hard-working and likes to improve. He's listening. he tries to show his commitment, he can play different positions - No.9, 11, 7, he can play with two strikers.
"There's a lot of possibilities with Dominic in the team. He's making big steps from last season."
Calvert-Lewin has scored three goals and registered five assists in 11 appearances this season.