Anthony Martial's next goal will cost Manchester United £8.5m

One of the clauses in Martial's contract requires United to pay Monaco £8.5m once the player reaches his 25th competitive goal for the club - a tally he is now one strike away from

Martial celebrates after scoring against Watford at the weekend (Getty)

Manchester United are set to pay £8.5m to Ligue 1 side AS Monaco the next time Anthony Martial scores due to an inserted clause in the player’s contract.

The Frenchman joined United in September 2015 for an initial £36m to become one of the most expensive teenagers in English football history.

However, it later emerged a series of clauses were written into the contract triggering payments as the Frenchman reached specific milestones at the club.

One such clause stated that United would be required to pay £8.5m to Martial's previous club once he reached his 25th competitive goal for the side.

And after adding United's second in their recent 2-0 victory over Watford, the Frenchman is now just one strike away from reaching this tally.

If his performance at the weekend is anything to go by, in which he plagued the Hornets relentlessly until his 80th-minute substitution, it’s simply a matter of time before United hand over the £8.5m fee to Monaco.

Martial’s overall price-tag could potentially increase to £63m on account of two more clauses which were inserted into the player’s contract on arrival at Old Trafford.

United can expect to pay an additional £8.5m once the Frenchman reaches his 25th international appearance for his national side, taking the transfer fee to £53m.

One final payment, worth £10m, will be scheduled should Martial be shortlisted for the Ballon d’Or, bringing the total transfer cost to £63m.

Despite the prospect of a £8.5m payment looming, manager Jose Mourinho was full of praise for the youngster in the wake of United’s Premier League victory against Watford.

"The Anthony Martial I want is the Anthony Martial of the last two weeks of training… and performs naturally the way he did today – or better because I think he misses a bit of confidence,” he said.

"But he is working very well and I gave him the chance to start."