The Red Devils have made a disappointing start to Mourinho’s third season in charge of the 20-time English champions following four defeats in their opening 12 games.
Manchester United’s 3-1 loss to Premier League leaders Manchester City in the derby at The Etihad last Sunday left the Red Devils in eighth place in the table and 12 points behind the Citizens.
While some top attacking players such as Alexis Sanchez, Romelu Lukaku and Marcus Rashford have struggled for form so far this term, there can be no doubt Manchester United’s biggest problem is their defence.
The Red Devils have already conceded 21 times in 12 games in the Premier League – only Fulham, Cardiff City, Burnley and Huddersfield Town have a worse defensive record than Manchester United.
Eric Bailly has fallen out of favour under Mourinho following his erratic performances, and English duo Phil Jones and Chris Smalling have struggle to convince that they are the long-term answer at centre-half.
Victor Lindelof, who moved to Manchester United in a £30m deal from Benfica in the 2017 summer transfer window, is the only defender to emerge with any real credit from the opening 12 games.
Pearce, who was one of the Premier League’s most feared defenders during his playing career, believes Mourinho needs to make improving his back four a priority.
“The goals at the weekend…” Pearce told Sky Sports’ The Debate on Tuesday night.
“Shaw switched off at the back post. Lindelof has been done by a give and go by Aguero. Aguero isn’t a speed merchant. It has gone above the goalkeeper and the goalkeeper has to do better.
“The goals against column is the one thing Mourinho will look at and think he has to address it first.”
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news