Anthony Martial could eventually cost Manchester United £61.6m, according to documents leaked on the Sport24 website.
The French forward joined Louis van Gaal's side in September from AS Monaco for £38.5m, a world record fee for the transfer of a teenager.
That cost could eventually balloon by a further 70% if all of Martial's add-on clauses are met, the leaked transfer document suggests.
The initial transfer fee comprised a payment of £15.4m due immediately after completion of the deal, with the remaining £23.1m due on July 1 this year.
Monaco will be due a further £7.7m if Martial reaches a 25-goal milestone during his United career, plus another £7.7m if he receives a FIFA Ballon d'Or nomination. A final add-on of £7.7m will be payable if Martial reaches 25 caps for his country from his current six.
