The defending champions were uncharacteristically dominated in their Group B opener, to put themselves in a likely must-win situation for their next two matches in order to reach the elimination stages.
The 34-year-old Xavi says "this is the hardest loss of my career. It was a terrible match, a debacle. We did everything wrong."
The Barcelona midfielder, who was making his 134th appearance for the two-time European champions, has won 26 major trophies in his career with club and country including three Champions Leagues and seven Spanish leagues.