The Catalan giants were beaten 2-1 by the Scottish champions at Parkhead in the fourth group stage match of the Champions League season but the Spanish ace says they cannot look back at that shock defeat with a trip to Russia coming up on November 20.
"The important game now is when we go to (Spartak) Moscow," Xavi told reporters.
"You have to be top of the group. We missed the opportunity to do that [against Celtic], but we depend on ourselves.
"We have to go and seek victory in the two remaining games."
Barcelona still sit on top of the Group G table despite the result but are only two points clear of second-placed Celtic whilst Benfica and Spartak Moscow are outside chances of qualifying for the knockout phase.