Anthony Martial could become Manchester United's record signing if certain benchmarks for add-ons, like being shortlisted for the Ballon d'Or, are reached.
Changes to the pound-euro exchange rate mean he could replace Angel Di Maria, who cost £59.7 million from Real Madrid in 2014, as United's biggest buy.
But the French forward will have to be named among the world's three best players, and reach two other milestones for that to happen.
When United signed Martial in September, his proposed cost if add-ons were triggered was £58.8 million, but that has swelled to over £60 million as the pound, which was worth €1.36, is now worth €1.29.
United agreed an initial £36 million (€50 million) fee for the striker, whom they made the most expensive teenager in the history of football.
They have already paid €20 million, which is guaranteed to go up to €50 million with another €30 million due to be paid by July 1.
United will end up paying a further €10 million if Martial scores his 25th competitive goal for them, another €10 million if he wins his 25th French cap and €10 million more if he is shortlisted for the Ballon d'Or, which would take his overall fee to €80 million.
So far, he has scored eight goals for United and has won six caps for his country.
Monaco revealed in the summer that Martial's move could bring them in €80 million and documents posted on the Football Leaks website confirmed that.