The 56-year-old has been instrumental in Bilbao's current campaign and Amorrotu has admitted that the club are desperate to offer the coach a new deal before his current contract expires at the end of the season.
"This is a coach who has improved all of the players, not just the team," said Amorrotu. "We need to find an agreement because it is fundamental for the consolidation of all that he is doing.
"And I have to say that the super-professional relationship with Bielsa is still being maintained and strengthened.
"He has taken on the role that we were all hoping he would, and he is giving us a lot of lessons that will serve us well for the future of Athletic."