I think fans of these two teams are looking the teams differently as if one is better than one when it comes to performance. These two teams are doing well, just that for a longtime now Barcelona and Manchester United have not meet and people just feel one is stronger than the other, atleast by the end of the match we can all see the performance of this teams and give accurate analysis from what has been seen from their performance.
it's natural for fans to praise their team because after all the fans will be at a crucial point to praise the opposing team. barcelona after the arrival of lewandowski in the transfer window last summer barcelona seems to have found its best form in Laliga this season. Same is the case with Manchester United where the arrival of Erik as their coach was able to make Manchester United strong again in the Premier League.
so it's hard to guess who will be the winner in the Europa League knockout round match. Rashford this season has had a very good performance with Manchester United in the domestic league, I think he is a player that Barcelona defenders will be wary of.