The £700,000 is thanks to a clause in the agreement reached between United and Real in the summer.
A Real director told Marca: “If Ruud is able to finish the top scorer in the Liga then we will have to find the amount that we must pay.
“We’d be happy, though, as it would mean that he would have scored a number of around 25 goals and with that amount we would be speaking about us being close to being champions of the Liga.”