Xabi was the favourite to succeed Jurgen Klopp at Liverpool, but committed to Bayer last week.
"If (Carlo, Real Madrid coach) Ancelotti steps down after next season, Xabi will have had another year to gain experience," he told AS.
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"The Real Madrid job will always be on the horizon.
"Xabi has a house in Madrid, and has a history at the club. In a few years you don't know what will happen in Bayern Munich or elsewhere, but in Madrid he would have a place.
" Will PSG look for a new coach? Will Pep Guardiola be at Manchester City in two years? You never know. It is the right decision by Xabi to stay at Leverkusen for another year, and put an end to the rumors for now."