Shearer wrote in his column in The Sun: "Manchester City wasted a golden opportunity last summer. Lining up against them will be the one who got away — United's Robin van Persie — who has proved to be one of the big differences between the two neighbours in this campaign.
"Roberto Mancini and his title-winners had missed a trick when the transfer window shut last August. When you are in a position of strength, you have to make the most of it.
"That was their big chance to bring in a couple more of the world's best players to really raise the bar. But, sadly for them, they did not take it."