Unless the Foxes experience a dramatic reversal of fortunes only Arsenal, Chelsea, Everton, Liverpool, Manchester United, Newcastle, Tottenham Hotspur and West Ham will remain members of that exclusive club.
City are one place above the drop zone after substitute Iain Hume had earned them a dramatic late equaliser.
The home side had started well with Lee Hendrie firing over from 20 yards before City threatened twice in a few moments.
First Dean Gerken had to punch clear while under pressure from Dudley Campbell, before Matty Oakley's goalbound drive struck a defender.
They continued to press but found Gerken in a determined mood when he dashed from his line to foil Campbell, who had outstripped the U's rearguard for a clear run on goal.
Matt Heath then almost headed through his own goal with David Bell's resultant corner creating mayhem in the penalty area, but with no Leicester player able to apply the finishing touch, Colchester were grateful to scramble the ball away.
The one-way traffic continued towards the visitors' goal with Patrick Kisnorbo hooking a shot wide and Richard Stearman driving directly at the keeper.
The final chance of the first half fell to the Foxes, with Gerken again swiftly off his line to foil Campbell after he had latched on to a Hendrie through-ball.
Barry Hayles thought he had broken the deadlock on 53 minutes but his header from Bell's cross was ruled narrowly offside.
Steven Howard's weak attempt on the hour mark was gathered comfortably by the keeper as the home side laboured to convert their possession into goals.
Paul Henderson prevented Colchester from taking a shock lead on 67 minutes when he had to be at full stretch to tip over Kevin Lisbie's deflected shot.
On 70 minutes, City sought to sharpen their cutting edge with Hayles and Howard making way for Hume and Matt Fryatt.
And the switch almost paid instant dividends with the visitors having to rely on a last-ditch tackle from Karl Duguid to deny Campbell after a flowing move involving both substitutes.
But it was Colchester who stunned Leicester on 76 minutes when they failed to block a Johnnie Jackson cross from the left which Lisbie headed home at the far post.
Leicester went close to levelling five minutes from the end when Gerken was compelled to beat away a Fryatt shot with Stearman heading the rebound wide.
Fryatt was then sent racing clear by substitute Gareth McAuley, but again Gerken was quickly off his line to deny the home side.
The Foxes appeared down and out, but a minute from the end Hendrie nodded on a Stearman cross for Hume to spring the offside trap and score with a stooping header.