She was reportedly rushed to hospital with a suspected stomach ulcer and missed Saturday night's show, which saw her last remaining act, Andrea Faustini leave the competition in third place.
A spokesperson for the star told MailOnline when asked if Mel would be back for the last programme: 'We're not sure yet.'Former X Factor judge, Tulisa Contostavlos filled in for Mel om Saturday and it is thought she will do the same again on Sunday night's show if Mel is unable to take up her position on the panel.
Tensions are set to be high on the popular ITV1 talent show, with Simon Cowell's two remaining acts, Ben Haenow and Fleur East, battling it out for the top spot.
It's been a dramatic few days for Mel B and things have kicked up a notch with a desperate Twitter plea from her sister Danielle Brown, 26.
Mel, 39, is reportedly receiving treatment for a suspected stomach ulcer which left her 'screaming in agony' and led to her chauffeur rushing her to hospital prior to an X Factor press conference and rehearsal session on Thursday afternoon.
And now her estranged sister, who fell out with Mel over her concerns about the former Spice Girl singer's husband Stephen Belafonte, has launched a Twitter tirade calling for Stephen, Mel's fellow X Factor judge Simon Cowell and even her PR firm, to get in touch with the family about her condition.
Danielle began by retweeting her mother Andrea's message and adding a few words of her own. '@ANDREA_m_BROWN: Mothers worse nightmare to hear ur daughters seriously Ill in hosp and not know where to go!!' It's just horrific!!!!!!,' it read.
Then she launched into numerous tweets, revealing her worry and fears over Mel's condition.
'This is ridiculous and cruel !!! Evil ! How can NO one tell me and my family where my sister is and what is going on?????
'Just a simple call to say she gonna be ok is all it takes!!!!,' she wrote.[sic]
Then she directly addressed Simon Cowell, who is reportedly extremely worried about his fellow judge.
Danielle wrote: '@SimonCowell How can NO one tell me and my family where my sister is and what is going on????? Can you please help? Or who can we contact?'
And then she moved on to Stephen, with whom she has always had a frosty relationship.
Danielle wrote: 'STOP @stephenthinks1 with your evil lies!! You told me and my mum yesterday she is fine and not in hospital @SimonCowell just doing press!
'@stephenthinks1 and now you say she is sick but ok Where is my sister??? What have you done??
'@stephenthinks1 if I have 2go press I will! Ive recorded all your calls 4 the past week including your 330am abusive call and Mel visit 2dad.'
The meltdown ended with a 'desperate' plea for help.
She tweeted: 'I am beyond desperate and this should be a private family matter!! But we don't know what else to do if anyone at all can help then pls do!'
Meanwhile, it is believed that the quick reaction of Mel's driver on Thursday were instrumental in getting Mel the medical help she needed.
Sources told The Sun on Sunday that her quick-thinking driver raced to an undisclosed hospital, where Mel is thought to be undergoing tests for ulcers and viruses in a bid to determine the exact cause of her sudden illness.
A friend said: 'Mel is in a terrible state, physically and emotionally. She is very weak and is being given treatment to help her with the pain.'
And the source claims source Mel 'could have died' were it not for her chauffeur.
There are varying reports about Belafonte – the father of three-year-old Madison, her third child – with The Sun claiming, 'Nobody knows where Stephen is,' while The Sunday People says he has been by her side throughout.
And Simon Cowell is said to be extremely worried.
A source told The Sunday People: 'Everyone is very worried. Simon has been in constant touch with her husband to keep updated. Simon hasn't spoken to Mel because she can't use her phone but has been fully informed about her condition.'
A source added to the Sunday Mirror: 'Simon has admitted to being very, very worried about Mel. She is such a livewire - everyone is really stunned at how quickly this illness took hold of her. Simon is in shock - we are all in shock.'
The dramatic episode has cast a dark shadow over the final, with former judge Tulisa Contostavlos stepping in at the eleventh hour for ailing Mel on Saturday evening.
But her arrival couldn't prevent Italian singer Andrea Faustini, Mel's one remaining contestant, losing out to Ben Haenow and Fleur East for a place on Sunday's show, during which the winner will be announced.
'Nobody thinks there is the tiniest chance of her making it back,' the source added. 'She is just far too fragile. Even if she was discharged from hospital today she wouldn't have the strength to appear.'
On Saturday Mel's mother Andrea Brown, with whom the former Spice Girl is estranged, tweeted: 'Mother's worse nightmare to hear ur daughter's seriously ill in hosp and not know where to go!!'
According to the source Mel's closest friends initially struggled to determine how serious her condition was because she wasn't answering calls.
When it became clear she was too unwell to make the first part of this year's final, N-Dubz star Tulisa – labelled the 'super-sub' by host Dermot O'Leary on Saturday night – was drafted in.
The incident is thought to be a huge blow for Mel, whose debut year has otherwise been a huge success, with fans warming to her direct approach.
The source added: 'She felt at the top of her game. Those around her are now just hoping she can bounce back.'
MailOnline have contacted Mel B's representatives for further comment.
