The Blaugrana were beaten by the Scottish champions at Celtic Park on Wednesday night and the Spain international believes they must get the loss out of their system and focus on their trip to Russia on November 20.
“The important game now is when we go to 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.”
Following the clash with Spartak, Tito Vilanova’s side host Benfica at Camp Nou on December 5 and remain top of Group G with nine points, despite their defeat in Scotland.