Barca must win this match over Inter, but if they lose. Barcelona is unlikely to have any chance of qualifying for the next round. Xavi's attention will automatically be devoted to the La Liga trophy.
Right now, getting full points against Inter Milan is more important to Xavi than a win against Real Madrid. Because if Barcelona lose against Inter Milan in the Champions League, their qualification for the round of 16 will be completely uncertain. Barcelona will surely want to have a first round exit from the Champions League despite having such a strong squad. I believe Barcelona will play well today and get 3 points against Inter.
Barcelona's attacking players will definitely need to perform well if they want to earn full points against Inter. Because in the last two matches of the Champions League, Barcelona has not been able to score any goals. Barcelona lost two matches due to poor performances from the attacking lineup's players.
Real Madrid is quite important to win because there is prestige there but when you see the league is still far away and there are still many opportunities then it is better for them to focus on the Champions League.