Watford have sacked manager Quique Sanchez Flores after Saturday's 2-1 loss to Southampton, saying "ultimately results have dictated our decision".
Chris Hughton is a possible successor and the Hornets said a replacement will be appointed "imminently".
Sanchez Flores, who was in charge for the 2015-16 season, was reappointed on 7 September, replacing Javi Gracia.
But he won just one of his 10 league games in charge with Watford bottom of the Premier League.
In an open letter to Watford fans published on the club website, the 54-year-old Spaniard said the club "will always be in my heart".
Watford have eight points after 14 games and are six points from safety - their worst return at this stage of a Premier League campaign.
"Quique is a man of great integrity and it was clear how much he wanted to have a positive impact, but ultimately results have dictated our decision," said chairman Scott Duxbury.
"The appointment of a new head coach is imminent, and with nearly two-thirds of the season remaining, we will provide all the support necessary to make the coming months successful."
During Sanchez Flores' latest spell in charge, they have only beaten Norwich in the league, while losing to Wolves, Chelsea, Burnley and Manchester City, where they were hammered 8-0. They were also knocked out of the Carabao Cup by Everton in the fourth round.
Since Gianfranco Zola's exit in December 2013, Watford have had nine managers, including Sanchez Flores twice.
Fellow Spaniard Gracia had been in charge for 21 months - making him the first Hornets boss to last more than one full season since Zola.
Sanchez Flores becomes the the third Premier League boss to be sacked in the past two weeks, following Unai Emery at Arsenal on Friday and Mauricio Pochettino at Tottenham on 19 November.
Watford are in their fifth season back in the Premier League since promotion in May 2015.
Gracia had led the club to the FA Cup final last season where they lost 6-0 to Manchester City, as well as 11th place in the Premier League.
They also reached the FA Cup semi-final in 2016 during Sanchez Flores' first spell as manager.
Analysis - 'Watford can't get next appointment wrong'
BBC Sport chief football writer Phil McNulty
Watford gambled by bringing back Sanchez Flores as manager in September - but have reacted with typical speed after realising the decision has failed.
For all the perceived managerial instability, Watford have a stable set-up behind the scenes overseen by the Pozzo family and chief executive Scott Duxbury. They realise that Premier League status is everything to a club that has worked so hard to achieve it.
This is why Gracia was sacked after losing three of his first four games this season and why Sanchez Flores has followed him after less than 90 days.
Watford are rarely caught without a plan when it comes to managerial succession. Sanchez Flores' appointment was announced 30 minutes after the departure of Gracia.
This will be arguably the most important decision the club's hierarchy will make.
Watford will appoint their third manager this season before the turn of the year and they know, with the Hornets bottom of the table with only eight points from 14 games, that if they get it wrong they may well be sealing their return to the Championship.