#2 Defensive depth
One of the main strength of Barcelona this season has been their defence and the depth in the rearguard. Under the tutelage of Ernesto Valverde, Barcelona's structure is more rigid and the defensive lines are getting harder for opponents to break down.
With the veteran center back, Gerard Pique, leading the Blaugrana rearguard, they have made fewer mistakes at the back. The team is much more comfortable defending than they used to be and catching opponents out on counters in the process.
Despite the long term injury of Samuel Umtiti, Clement Lenglet has stepped up and shown his potential against the toughest opponents in the season so far. Moreover, Barcelona's second choice goalkeeper, Jasper Cillessen, is much more reliable and can do wonders even in the absence of Marc-Andre Ter Stegen.
Defense plays a major role in the season and Ernesto Valverde is clearly making it a priority, which will only benefit the Blaugrana in their quest for European glory. Despite Manchester United's attacking prowess, it is expected that Barcelona's defenders can cope with the pressure.