Porto paid Watford €500,000 to sign Miguel Layun on loan with the Portuguese club having the option to sign him permanently for €6million this summer, according to a document released by website Football Leaks.

Layun joined Watford in January 2015 from Club America but spent just eight months with the Hornets before leaving for Porto in the final days of the summer transfer window.

It was a surprising switch but, as usual, Watford ensured they got the best deal possible.

The €500,000 loan fee - around £385,000 - was to be paid in two instalments.

Half of which was paid on September 30 and the other half being paid on January 31.

Should Porto wish to make the deal permanent this summer they would need to notify Watford by May 31.

The club would then pay €3 million within 15 days of exercising the option and a further €3 million paid on July 31, 2017.

Watford also negotiated a 20 per cent sell-on clause in the deal if Layun is sold by Porto for a fee exceeding €6.5million.

Since moving to Porto Layun has made 28 appearances for the club, six of which were in the Champions League.