The Argentine midfielder has impressed in his debut season, with four goals and five assists in 32 Premier League appearances.
Now the Evening Standard there is interest from another major European club in signing Mac Allister in the future.
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It's claimed there is a buyout clause in Mac Allister's contract, which Spanish giants Real Madrid are considering using.
The clause is said to be set at 60m.
It is not clear whether Real Madrid will make an attempt to sign Mac Allister this summer - but offers are expected within the next year.