Shearer wrote in The Sun: "A fortnight ago he was being hailed for outwitting Alex Ferguson at Old Trafford to win his third Manchester derby in four in the league.
"Now suddenly he is not the man to drive City on next season in some people's eyes.
"People jump to these judgments and I just hope the City owners don't do the same.
"A lot of Mancini doubters base their views on this season.
"Yet in his three full seasons in charge Mancini will, in all likelihood, have finished third, second and first and delivered two FA Cups.
"That, for me, in such a short space of time is success."