Watford have sacked Quique Sanchez Flores less than three months after bringing him back for a second spell as head coach.
The Premier League club announced the decision on Sunday, the day after a 2-1 loss to fellow strugglers Southampton.
Watford surrendered a first-half lead at St Mary's and remain rooted to the bottom of the table with eight points from 14 games.
In a statement issued on their official website, Watford pledged to move swiftly to install Flores' successor.
"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 and chief executive 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."
Flores, who presided over a creditable 2015-16 campaign, only returned to Vicarage Road in September after more than three years away.
He replaced Javi Gracia after a slow start to the season but was unable to rectify poor results.
The former Valencia and Atletico Madrid boss took charge of 12 games in all competitions for two wins, four draws and six defeats, including the humiliating 8-0 loss to Manchester City.
Former Newcastle United and Brighton and Hove Albion boss Chris Hughton is rumoured to be one of the frontrunners for the Watford post.