Shearer wrote in The Sun: "Until Saturday, I was sure they still had a chance of retaining their Premier League title.
"After all, I tipped them to do just that and did not have any great concerns as the gap at the top of the table between City and United stretched a little.
"But their display in the 3-1 defeat against Southampton has told me there is no coming back now.
"Things have got steadily worse over the last fortnight.
"Fast forward to St Mary’s and it is no exaggeration to say that Saints could have had four or five goals.
"City’s passing was awful, their defence shambolic and decision-making simply wrong.
"This from the team with the best defensive record in the league, a side that had not conceded in January.
"The simple truth is that, without Vincent Kompany, they look rudderless at the back."