The Hornets, who sacked Javi Gracia earlier in the season, now find themselves six points from safety and in dire need of change as they seek to appoint their third manager of the campaign. They have won just once in the league so far this season.
Watford Under-23 coach Hayden Mullins and head of academy goalkeeping Graham Stack will oversee training on Monday morning at Watford ahead of their game at Leicester on Wednesday.
Watford hope to make swift progress in their recruitment of a third manager this season following Wednesday's clash with high-flying Leicester. Flores left Watford for the second time following Saturday's 2-1 defeat at fellow strugglers Southampton.
Mullins, the former Crystal Palace, West Ham United and Portsmouth midfielder, joined Watford's coaching staff in 2016 and will look to guide them to their second league win this season.
The decision was taken after Sanchez Flores met with chief executive and chairman Scott Duxbury along with owner Gino Pozzo on Sunday, with the appointment of a successor described as "imminent".
He replaced Javi Gracia after a slow start to the season but was unable to rectify poor results.
A run of six defeats in 12 games in all competitions also included an 8-0 thrashing at the hands of Manchester.
Following his final game in charge, Sanchez Flores said he was "sad if he can't help the team".
"It's the way I chose, I can't do anything for that". I can't regret for that. This is not me, it's not my character. If I stay in my comfort zone it's not me. "I came here and I'm trying and fighting a lot, although the circumstances are bad for us".