#2 Recent history does not favour Barcelona
As already established, Barcelona have been eliminated at this stage of the Champions League in each of the last three seasons consecutively, and four times out of the last five.
This poor run started in 2014 when Atletico Madrid knocked out the five-time winners 2-1 on aggregate after drawing 1-1 at the Camp Nou and winning 1-0 at the Vicente Calderon.
Two seasons later, lightning struck twice as the Rojiblancos once again eliminated the Blaugrana, and a season later it was Juventus's turn as the perennial Italian champions knocked Barcelona out with a 3-0 aggregate victory.
The low point unarguably came last season as Barca somehow found a way to throw away a 4-1 first leg lead to lose 3-0 at the Stadio Olimpico against Roma to once again get dumped out of the quarter-finals.
Roma's heroics last season would undoubtedly give Manchester United some confidence that they could also pull off a shock and as such, Barcelona would be desperate to avoid a repeat.