Quique Sanchez Flores has been sacked by Watford less than three months after returning to the club for a second spell in charge.
Watford lost 2-1 to relegation rivals Southampton on Saturday and sit bottom of the Premier League, six points from safety.
"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," Hornets' chairman & CEO Scott Duxbury said.
"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."
Watford are now set to name a 10th manager since 2013.
Sources have told ESPN FC that Chris Hughton and Paul Clement are among the candidates to replace Sanchez Flores, who oversaw just one win in 10 Premier League games.
The Spaniard was previously in charge of Watford during the 2015-16 season during which he led the club to an FA Cup semifinal and a 13th place finish in the Premier League.