Aymeric Laporte is in Manchester ahead of a club-record transfer to Manchester City in a deal worth £57m.
The France U21 international issued a farewell message all those involved with the Basque club in a post on their Twitter account, thanking team-mates and fans for the time they had shared during his six-year spell at the club.
City will pay Laporte’s £57m release clause, which would break the club’s transfer record of £55m that they paid for Kevin De Bruyne from Wolfsburg in 2015.
The central defender, who has made 19 appearances for Athletic this season, was left out of their squad to face Eibar on Friday.
Jon Driscoll and La Liga expert Terry Gibson take a look at Aymeric Laporte, the latest player set to join Pep Guardiola at Manchester City
Sky Sports News reported last week that discussions had begun between the clubs over a deal for the 23-year-old.
Pep Guardiola refused to give anything away when asked about their pursuit of Laporte, but it appears they have now persuaded the Spanish club to part company with the player.
Asked whether Laporte was a player of interest, Guardiola said: “There were players in the past who we were interested in and we will be in the present and the future.
“I always try to do the best for the club; knowing the players that we have and knowing the players that can improve our squad.”
Laporte previously turned down a move to the Etihad in October 2016 but the Premier League leaders have always remained interested.