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.
