He also claims the Red Devils are in disarray in regards to tactics and Mourinho knowing his best team - the complete opposite to Pep Guardiola's champions.
Shearer said: It has been a long time since anyone won back-to-back titles but I think City will win the Premier League again because of Pep - he won't want their standards slipping.
"The manager is obviously not happy about the signings he hasn't been able to make and not having certain players available on their pre-season tour, which isn't nice to hear if you are a young kid trying to make your mark on the fringes of the squad".
"But he's got great experience, he's been at top clubs, he's been in hard positions before, he's in a hard position now I think, but he needs to try to find a way to get out of it".
Whether they can do it across a 38-game season, however, is the big question.
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It's what the team lacked - someone who plays "jogo bonito", as they say in Brazil. If his team don't do well, if they're not playing well, if they're not entertaining people, they're not challenging for the league, then he possibly could go.
Jose Mourinho said on Thursday that he did not expect United to add any more players before the Premier League's 5 p.m. BST transfer deadline that day, meaning Brazil midfielder Fred, 19-year-old full-back Diogo Dalot and reserve goalkeeper Lee Grant are the only additions to the squad.
"The other clubs who compete with us are really strong and already have fantastic teams".
"But Gundogan I like as a player with a special feeling in the box".
"Or they are investing massively like Liverpool, who are buying everything and everybody".
Alexis Sanchez sees Manchester United's Premier League opener against Leicester on Friday as a "must-win" game.