According to The Sun, Ronaldo triggered a bonus-related clause in his contract after hitting 21 goals for the season.
The deal the 37-year-old signed last year on his return to Old Trafford, includes a £750,000 bonus for reaching 20 goals plus a further £100,000 for his hat-trick strike.
Ronaldo will now receive £100,000 for each further goal he scores for the remainder of this season.
United will also pay their top scorer this season £1million and the Portugal captain seems almost certain to be the beneficiary, as he is 12 goals ahead of his closest challenger Bruno Fernandes.
Also, Ronaldo would receive around £2.75million in total payments if he manages to reach 30 goals this season.