Liverpool were thumped 4-0 on the day, with traveling fans flooding for the exit at the Etihad well before the final whistle.
Writing for the Liverpool Echo, Aldridge said: "What I saw at the Etihad on Saturday afternoon was something I'd never experienced watching or playing for Liverpool FC.
"Never have I ever witnessed that many fans walking out in protest at a performance or a result with so much time left to play in a game.
"Manchester City were 4-0 up with around a third of the FA Cup tie left to play when many of those who had made the journey across the M62 for one of the shortest away-days of the season decided for an early dart.
"Many of them were probably back in their locals on Merseyside by the time the final whistle went in Manchester and the players owe them an awful lot now going forward.
"These are the same supporters who made the cross-country trek to Brighton for a 12.30pm kick-off only a fortnight earlier, many of them getting up at 4 or 5am to make the trip.
"That will have cost fans upwards of £2-300 and given what has been served up to them, I can't blame them for voting with their feet. These fans have to work hard to put food on the table for their families and then they are given these sorts of performances back, it is unacceptable."