It was expected that Krastev, 18, would sign for City then head to their partner club Lommel on loan.
However, it appears that City have been bypassed completely with Lommel announcing Krastev as their player today.
He has signed a long-term deal with the Belgian second division side until 2025.
Lommel also revealed that he will return to Slavia Sofia on loan until December, after which he will link up with his new team-mates.
Bulgaria under-19 international Krastev made his first team debut for Slavia aged just 16.