Former Manchester City defender Danny Mills says the club "missed a massive opportunity" to close the gap on Liverpool at the top of the Premier League when they lost 2-1 to Newcastle United on Tuesday night.
A victory against Rafa Benitez's team earlier this week would have put the champions within a point of catching Liverpool at the top of the league.
After the 2-1 loss at St James' Park, Pep Guardiola admitted his side "were not at their best", but added that the title race is far from over with 14 games to go.
Former right-back Mills, who made over 50 appearances for the Sky Blues, believes that City may regret not being clinical enough against the Magpies.
"They scored after 23 seconds and you think is it going to be three, four? They didn't kick on, They never put them [Newcastle] to the sword, which is not like them at all.
"Newcastle were resolute and made them pay on the counter-attack and it's a massive blow for City who could have put the pressure on Liverpool.
"Complacency could have been a factor the other night, all of a sudden you get to half time, it's one nil and Newcastle have a bit of belief. It was a huge opportunity missed.
"It doesn't take the top sides a lot for them to become normal almost, maybe even a 5 to 10 per cent drop off.
"For Manchester City and Liverpool this is now all about pressure now, and who can deal with it best."
The second-placed side will be looking to bounce back from their fourth defeat of the campaign when they face Arsenal at the Etihad Stadium this weekend.
Sergio Aguero has scored in seven of his last 11 matches against Arsenal in all competitions, and Mills believes he could make the difference against the Gunners this weekend.
"In and around the box his movement and his sharpness is class, when he plays for Man City he adds a different dimension.
"He is three or four years ahead of where Jesus wants to be, if he's fit he is first name on the teamsheet."