The Bavarians are desperate to lure the 23-year-old to the Allianz Arena, but his current club have no intention of letting him go for anything less than his buy-out clause.
Effenberg hopes that the midfielder will make an instant impact at Bayern if the move materialises, but he has his doubts about the Bilbao star's potential.
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"It has surprised me a bit that Bayern are so desperate to get him. He is not even a regular starter for Spain. Yes, he has won the World Cup and the Euros, but he played only 25 minutes at Euro 2012.
"It's clear that he's not on par with the big guns like [Andres] Iniesta and Xavi. That's why I'm wondering whether he's worth the money."
Bayern sporting director Matthias Sammer stressed on Wednesday that the transfer is by no means a done deal yet, but talks remain ongoing.