MU is not so bad, but I think Barcelona does have a chance to win the game.
Barcelona has a chance to win the game so does Manchester United. No club is actually too stronger than another and wining chance is sort of balancing for two clubs.
Even at the European level, it seems that the strategy implemented by Xavi still cannot work over to the European League, seeing that MU is currently in a not good mental condition. Indeed, there is still time for MU to improve their performance and strategy, but in otherside Barce will also improving their performance within this 2 weeks. I think barcelona can manage 1 goal to get 3 points.
Xavi is a young coach with limited experience in Champions League and Europa League and his club has more issues when playing in Champions League and Europa League than playing in La Liga. Xavi does not have too good ability to make his tactics more flexible to use in Europe and can not solve challenge from clubs that come from different nations. When they are from other leagues, not from La Liga, Xavi and Barcelona have bigger challenging opponents and usually they are failed to solve such math.