The defeat was Chelsea's worst since their 7-0 loss to Nottingham Forest in 1991 and will raise serious questions about the direction the team is going in under Italian Sarri as they slipped to sixth place on 50 points, a point off the top four.
The Chelsea manager oversaw a training session at Cobham on Monday that consisted of players that didn't start the game against City.
Eden Hazard went to sleep from Kevin de Bruyne's quickly taken free-kick and Bernardo Silva had acres of space to cross for the England global to fire home.
"We had only to stay in the match but the reaction was not good".
The former next play Crystal Palace, Brighton and Hove Albion in the next couple of weeks - they didn't beat any of those two in the reverse fixtures and would certainly not this time either because that's what Puel's Leicester do.
Aguero should even have had more, having missed a sitter in the early stages and headed against bar on a dismal afternoon for Chelsea, whose manager Maurizio Sarri headed straight down the tunnel at full-time.
The Spaniard cemented his presence in the Sarri camp by explaining: "People think if you buy players, you can immediately come in and win, but you need time". I don't have to convince him, he knows me. A team who have a history of playing until the last minute of the last game - of never giving up.
"He looks totally out of the role he played last season".
Guardiola fell to the floor in exasperation when Aguero somehow side-footed wide with his easiest chance of the game at 1-0.
"Aguero is just clever".
When asked what the future holds for Sarri, Blues legend Harris told Love Sport Radio: "That's for the powers that be [but if I were in charge] I would most probably have a chat with him and say "you've got until the end of the month to put things right and if not, you're obviously in a precarious position". "But his reaction was a little bit better".
Aguero had a simple task to make it 3-0 six minutes later when he pounced on Ross Barkley's slack header towards his own goal.
"It doesn't happen to Chelsea much, so when it does, it's a shock".
Aguero completed his hat-trick from the penalty spot after the break and Sterling finished the rout late on.
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