Manchester United are facing the Spanish side in their final friendly before the season starts.
And Erik ten Hag has used to it play several fringe players, of which Maguire now belongs.
Having already been stripped of the captaincy earlier this summer, the England international was also denied the armband despite new skipper Bruno Fernandes not playing.
Instead, Tom Heaton has been named captain this Sunday in Dublin at the age of 37 in yet another clear snub from Ten Hag to Maguire.
The defender was furious that he had lost his armband earlier this summer.
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Fernandes has been named as the new United captain while Maguire has been relegated to a bit-part role at Old Trafford.
"After discussions with the manager today he has informed me he is changing captain," Maguire tweeted last month.
"He outlined his reasons to me and whilst I'm personally extremely disappointed, I will continue to give my all every time I wear the shirt.
"So I wanted to say a massive thank you to the Manchester United fans for all their brilliant support whilst I've been wearing the armband."
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As well as Heaton and Maguire, several other fringe players have been named to face Athletic Bilbao.
Facundo Pellestri, Dan Gore and Donny van de Beek will play while new signing Rasmus Hojlund will have to wait for his debut.
The 20-year-old, who was signed from Atalanta for £72million, is facing a spell on the sidelines.
He picked up a knock while in Italy that will see him miss a few weeks of action just as the Premier League season gets underway.
Maguire has been linked with an exit from United this summer amid interest from West Ham.
David Moyes is keen on the former Leicester star but saw a £20m bid rejected outright by the Red Devils.
However, with Ten Hag keen to raise funds, the Hammers could return with a double swoop bid for Maguire and Scott McTominay.