Leeds United's Premier League relegation rivals sack manager ahead of Elland Road trip
Leeds United are 19th in the 20-team table so would have been looking at their next home game, against Palace on April 8, as an opportunity for a much-needed win.
Palace are 12th yet only four points ahead of Leeds, one of five teams below them with a game in hand.
It is 12 matches since Palace's last victory, at Bournemouth on New Year's Eve.
"It is with enormous regret that this difficult decision has been made," said chairman Steve Parish.
"Ultimately, results in recent months have placed us in a precarious league position and we felt a change is necessary to give us the best chance of retaining Premier League status."
The 46-year-old led the Eagles to 12th in his debut season at Selhurst Park with some attacking football but this term they have scored just 21 goals in 27 games.
Coaches Osian Roberts, Kristian Wilson and Said Aigoun have also left the club with no immediate announcement on who will take caretaker charge of Sunday's match at title-chasing Arsenal.
After that, the south London club have a fortnight's international break to step up their search for a new manager. They should be warned, however: relegation rivals Leeds and Southampton both sacked their managers in February and struggled to find a replacement.
The Whites were knocked back by the first four or five names on their list and ended up turning to former Watford coach Javi Gracia. When Southampton were unable to reach agreement with the man Leeds sacked, Jesse Marsch, they gave the job to caretaker Ruden Selles until the end of the season.