Porto, el Manchester City, Arsenal, Manchester United or Bayern Leverkusen
Although the Champions League final is already to be played this season, the finals of the main European Leagues helps us to draw how balls are for next edition of the 2015/16 season.
One of the news of next year is that the Ball 1 will include all champions of the main European leagues (Spain, England, Germany, Italy, Portugal, France, Russia and Holland). On the other hand, powerful teams that didn't win their competition will be on ball 2, this is the case of Real Madrid, Manchester City or United.
With this view, Barça's rivals are in Ball 2 and they may be Porto, Manchester City, Arsenal*, Manchester United* or Bayern Leverkusen* (*The last 3 teams will access if they beat the classification round).
This 2nd Ball will also include Real Madrid, Atletico Madrid and Valencia* (*if they beat the previous round) but they won't be able to face Barça because they are two teams in the same home competition.
This is how is now the table of balls waiting to finish all the competitions (the italian league will be played this weekend) and the classification rounds of Champions will be played during summer.