Manchester United is performing poorly against strong clubs this year. I don't think they can win against Barcelona. This will probably be one of the most interesting matches. If Barcelona can beat Manchester United, we can probably say that they can win the Europa League. Especially since Barcelona is now playing better than Real Madrid in La Liga.
This game is unpredictable, I feel anything can happen. Despite Manchester united are not in a good shape, they are still trying to get improve. Manchester United with their current quality of performance they are capable in challenging Barcelona. This is a game anything of the team can luckily win.