Eintracht Frankfurt will need to pay extra if Donny van de Beek's loan proves successful.
The Manchester United midfielder has joined Eintracht Frankfurt on-loan to the end of the season.
A permanent deal worth €10m has been settled between the two clubs, but an extra €3m will be due if certain targets are reached by the Bundesliga club.
These bonuses include European qualification.
United paid Ajax €39m for Van de Beek in June 2020.