Williams has come through the ranks at Bilbao, where his older brother Inaki is also a player, and made his debut for the club aged 18 in April 2021.

He has scored 31 goals in 167 appearances for the club and helped them finish fourth in La Liga last season as they qualified for the 2025-26 Champions League.

Williams also helped Spain win Euro 2024, scoring in the 2-1 victory over England in the final.

This announcement comes after it was understood that Barcelona had agreed personal terms with the forward which led to Athletic fans erasing Nico Williams from a mural featuring him and Inaki.

It is also just over a week after Athletic said they had met with La Liga to find out about Barcelona's "ability to sign players" amid the Nou Camp club's financial issues.

Athletic Bilbao added they had "legitimate interest in accessing the relevant information after FC Barcelona sporting director Deco publicly acknowledged that they will try to sign a player from our first team".

"Deco's statements add to the public statements made by FC Barcelona president Joan Laporta himself, admitting that the Blaugrana club 'is working to be within the 1:1 rule' and that, therefore, it is not currently within the parameters of said rule for registering players."

The '1:1 rule' states that Barcelona can only spend as much as their income and accounts allow, with La Liga calculating a limit based on the club's expected income.