Liverpool are believed to have sought to have the match, which is due to start at 12.30pm on Saturday week, switched to a later time of 7.45pm in order to have a better chance of having their Brazilian duo available.
The pair are with their national team squad for their forthcoming World Cup triple-header, the final game of which is due to take place against Uruguay in the early hours of Friday, October 15 – less than 36 hours before the game at Watford.
The ECHO understands, though, the Hornets opposed the move given there is less than a fortnight before the game and many supporters will have already finalised travel arrangements.
It means Caoimhin Kelleher is on standby to make his second appearance of the season as deputy to Alisson in goal, while Liverpool boss Jurgen Klopp will have to look to midfield alternatives with Fabinho absent.
Both Brazilians will have to partake in a bespoke 10-day quarantine on their arrival back in the UK after a deal was struck with the Government that would allow players who have travelled to red-list continues to train and feature in matches provided they are fully vaccinated. Alisson and Fabinho are both double-jabbed.
The duo aren’t the only Liverpool players who will have to quarantine after the international break, with both Senegalese forward Sadio Mane and Greek defender Kostas Tsimikas featuring for their national teams in red-list countries.