Port Vale have sacked manager Andy Crosby after less than year in the job.
Vale have won just once in eight games to leave them 20th in League One, two points above the relegation zone - albeit with games in hand.
Assistant manager John Schofield will also leave his position.
Crosby had already taken over in a caretaker capacity when Clarke was off on compassionate leave - and led Vale out in the League Two play-off final at Wembley, where they beat Mansfield Town.
He also this season led Vale to the Carabao Cup quarter-finals, where they were beaten by Middlesbrough in December - the furthest they had ever been in the competition.
Vale made five loan signings in the January transfer window, although one of them, Rhys Williams, had to return to parent club Liverpool because of injury - and he also lost his two main loan signings, Sheffield United's Oli Arblaster and Tottenham's Alfie Devine, who were both recalled.
But, in Saturday's first game since, they lost 3-0 at fellow strugglers Fleetwood, to leave them just two points clear of trouble.
It is all in stark contrast to the start of the season when they won five of their first seven games to go second in League One. But they have won just three times in 20 league matches since.
Vale have not yet said who will be in caretaker charge for Tuesday's home game against Leyton Orient - but they say "the search for a new manager has already begun".
Timing of the decision a 'surprise'
Analysis - BBC Radio Stoke's Vale reporter Phil Bowers
The biggest surprise is the timing of this announcement coming so soon after the transfer window, which only closed on Thursday night.
Anybody coming in will have to work with the squad at hand, which is a squad that we already know is light on centre-forwards and is light in other key areas.
And it has also been upset by injuries. Two key players in Uche Ikpeazu and Ben Garrity, the top scorer.
But it's the run of just three wins in 20 games that has done for Andy Crosby. It's very similar to the three wins in 19 games before Darrell Clarke went.