Alesha Dixon has stepped in to replace the talent show judge, who has now flown back LA for treatment.
Sharon has been suffering with back problems in recent months, having undergone an operation after twisting it while playing with her grandchildren earlier this year.
However, The Sun has reported she is hoping to be able to rejoin the audition tour soon.
She was asked to stand in after impressing bosses when she sat in Nicole’s chair in Manchester on Saturday, when the former Pussycat Doll was unavailable due to prior work commitments.
An ‘X Factor’ spokesperson said: “Unfortunately, Sharon is suffering from niggling back problems following surgery earlier in the year and will be unable to take part in the Edinburgh auditions.
“Alesha will be guest judging on the panel today.”
It was originally feared Sharon’s on-going back problems could have ruled her out of this year’s series, but she surprised fans by signing up for another stint on the ITV talent show.
The judging line-up remains the same as 2016, marking the first time in seven years there have been no changes to the panel.
‘The X Factor’ is expected to return to ITV in the autumn.