The midfielder underwent a medical with the Germans without permission from his club, before completing his move the following day, and the Basque side are not amused with die Roten's behaviour.
"We are looking into the possibilities of taking legal action against Bayern Munich," Urrutia stated at a press conference.
|BILBAO BAGGING TOP FOUR?|
|4/1||Athletic Bilbao are 4/1 with Bet365 to finish in La Liga's top four|
Bayern Munich eventually met the player's €40 million [£32m] buy-out clause to lure the Spain international away from Bilbao and the 24-year-old made his official Bayern debut at the weekend in the 6-1 Bundesliga win over Stuttgart.