Bayern Munich sign Athletic Bilbao midfielder Javi Martínez

Bayern claimed that Martínez, 23, had rescinded his contract with Bilbao and been given permission to join them by the Spanish football federation and the professional football league.

"This was without question a complicated transfer so we are all the happier that Javi Maítinez is finally with us," Bayern CEO Karl-Heinz Rummenigge said of the deal, which has dragged on for several weeks.

Bilbao said Martínez, who has signed a five-year contract with the Budesliga side, travelled to Germany on Tuesday without their permission, Kazinform quotes the Guardian.

"Athletic Club would like to make clear that at no time did they authorise the trip their player Javier Martínez made to Munich on 28 August," Bilbao said in a statement on their website.

The club had asked the player for an explanation, the statement added.

Bilbao have made it clear they want to hold on to both the 23-year-old Martínez and his Spain team-mate Fernando Llorente, who has said he wants to leave and has been linked in media reports with a move to the Italian champions Juventus.