Constituents of Mr O'Mara in his Sheffield Hallam constituency have already taken to social media to express concern that the future of the UK could be decided in their MP's absence.
The former Labour MP has a difficult year which led to him announcing he would resign from the Commons in September, a plan he later postponed.
But he has missed a number of the key votes on Brexit during 2019, including the vote in September which led to the so-called Benn Act, requiring the Prime Minister to seek a Brexit extension if faced with a No Deal situation.
With the votes expected to be very close tomorrow, with some even predicting they could be equal with the casting vote going to Speaker John Bercow, Mr O'Mara's vote - or lack of - could be crucial.
One Sheffielder said on Twitter in response to a call to get MPs to back the The PM's deal: "I would if we had an MP (Jared O'Mara) who actually goes to the HoC and actually bothers voting! #SheffieldHallam."
Another Twitter user said: "I'm driving from Sheffield with others to #FinalSay march in London if Jared O'Mara would like a lift? Happy to help."
In July, Mr O'Mara announced he would step down after a series of problems which saw him suspended from the Parliamentary Labour Party and then resign from the party.
But the Treasury, which administers MP resignations, later announced that he had postponed this decision.
Mr O'Mara provided one of the shocks on the night in the 2017 general election when he ousted former deputy prime minister Sir Nick Clegg from his Sheffield Hallam seat.
But the new MP's political problems began a few months after his election when a series of sexist and homophobic online posts were uncovered which he had made when he was in his early 20s.
These included inviting the band Girls Aloud to an orgy and joking about the musician Jamie Cullum being "sodomised to death".
After further revelations he had the Labour whip withdrawn.
In December 2017, Mr O'Mara said he had scaled back his activities on the advice of doctors and later said he made three suicide attempts during his suspension.
Labour later said it had readmitted him but he then resigned from the party saying he had experienced "little to make me feel welcome, understood and accepted".
Describing himself as "the first autistic MP in our history", Mr O'Mara, who also has cerebral palsy, wrote: "I didn't commit any crimes, yet I have been made unfairly to feel like a criminal."Soon after this he again stepped back from his work in the Commons on doctors' advice.
In April this year, Mr O'Mara suspended case work in his constituency office for a month following reports all his staff had either been sacked or resigned.
In July, one of his staff, Gareth Arnold, used the MP's own Twitter account to resign in public and criticise his former boss.
Mr O'Mara responded with a lengthy statement, saying: "I will be taking time out to receive professional help to deal with my mental health and personal issues regarding self-medication."
Mr O'Mara used his statement to blame Labour leader Jeremy Corbyn for how he had been treated by the party.
The PA news agency was unable to contact Mr O'Mara on Friday.