Fairbrother was suffering from a calf strain and Hegg's thumb was still badly bruised - and both were rated extremely unlikely to play in a game where victory would send Lancashire four points clear at the top.
However Lancashire were hoping that captain Wasim Akram would be back in action after being sidelined for a week by a groin injury.
Paddy McKeown was called up to replace England star Mike Atherton and Burnley batsman Mark Harvey was on standby for Fairbrother.
Warwicks were expecting a 10,000 plus gate for the match which starts at 5pm.
Lancashire, second in the championship after their victory at Edgbaston on Monday, return there tonight on the path of a glorious treble.
The Axa League table toppers can end Warwickshire's challenge for the 40 overs title and at the same time assert themselves as short priced favourites to capture the title for the first time since 1989.
And next week they take on Yorkshire in the second round of the Nat West Trophy before embarking on the second half of the championship mme against Worcester at Lytham on July 14.