United battled back after falling 2-0 down at Old Trafford inside 10 minutes, scoring three times in the final 20 minutes to win 3-2. Goals from Juan Mata, Anthony Martial and Alexis Sanchez helped Manchester United to complete the comeback.
But the goal by the French forward cost United £7.7million, thanks to a clause in the deal which saw him move from Monaco in 2015.
According to Mail Online, United parted with £38.5m in two installments to sign Martial, but the deal included plenty of lucrative bonuses which meant it could have eventually cost as much as £61.6m.
One was that United agreed to pay Monaco an extra £7.7m if the Frenchman netted 25 goals in the Premier League before the end of the current 2018-19 season.
Monaco were waiting on the cash for 10 months before Martial struck against Newcastle. However, the goal count eventually ticked over to 25 on Saturday, and it may not be the last time United have to pay up.
There are two more clauses in Martial’s contract that can be triggered which would see United have to fork out another £7.7m each. One of these requires him to make 25 appearances for France – he is currently eight away, while the other would need him to win the Ballon D’Or
That means United have so far paid Monaco £46.2m for the 22-year-old.