According to Spanish publication 'Mundo Deportivo', the French forward fulfilled an agreement that was included in his contract when he signed for United from Monaco.
The clause stated that if Martial scored 25 goals, then United would have to pay the club €10m.
This money is in addition to the €50m that United originally paid to secure the services of the then-teenager in 2016.
Other clauses in the contract reportedly include a bonus if Martial reaches 25 caps for France (he currently has 18) or if he is ever nominated for the Ballon d'Or.
Martial scored the equaliser for United as they came from two goals down to beat Newcastle 3-2 at Old Trafford.