United had previously signed Carreras from Real Madrid's youth academy when he was a teenager, before selling him to Benfica last summer. Now, Real Madrid are interested in bringing Carreras back to the club and are seeking a favor from United in the process.

Real Madrid are willing to pay €35 million to acquire Carreras this summer, which is more than the €18 million that United can exercise the buy-back clause for. Benfica, however, values Carreras' buyout clause at €60 million.