Last season when eliminated to Europe League Barcelona failed reach to final stage after beating by unpredictable team Frankfurt~
Of course, they were eliminated, they couldn't reach the final round. 
It was very surprising, I still couldn't believe that Barcelona was defeated by Frankfurt.
this season have different with many bigger team actually eliminated from Champion League and have to play at Europe League. Juventus, Sevilla, and Ajax are team eliminated at Champion League could be strong opponent for Barcelona added have several team like Arsenal and Manchester United could make difficult how to reach final at Europe League.
Juventus and Sevilla are weak teams this season, I am sure Barcelona will have no difficulties beating them.In theory, only Arsenal, Man United, and Ajax have the chance to beat Barcelona. However, sometimes there is a surprise in football matches, unfavorite teams can beat favorite teams. Barcelona isn't impossible to repeat the same failure as previously. So, Xavi can't focus on the big teams only, they also must be careful with smaller teams.