#2 The defense of Manchester United might cause them to suffer
As of this writing, Manchester United find themselves at the sixth spot in the Premier League points table. Their other league opponents, notably Wolves, exposed their defensive vulnerability right after their solid win against PSG.
Defense is one of the areas where a team needs to be topnotch. Even without good strikers, a team can survive if they have a strong defense. Manchester United lack proper defenders to compliment the talented strikers of the side.
Against Lionel Messi-led Barcelona attack, the team really should focus more on their defense. Apart from being the best goalscorer, Messi had evolved into a brilliant playmaker this season, assisting 12 league goals.
It should be a priority for players like Victor Lindelof, Chris Smalling and Luke Shaw to bring their A game against the Argentine. However, singling him out might open room for other strikers as Barca have a literally unstoppable attack.