Sunderland on Saturday sacked manager Martin O'Neill, just hours after the club had lost 1-0 at home to Premier League leaders Manchester United to slip closer to the relegation trapdoor.
"Sunderland AFC has announced that it has parted company with manager Martin O'Neill this evening," said a club statement.
"The club would like to place on record its thanks to Martin and wishes him well for the future. An announcement will be made in the coming days regarding a successor."
The 61-year-old Northern Irishman was in charge at the Stadium of Light for just 16 months having succeeded Steve Bruce in December 2011.
But Saturday's loss to United left Sunderland just two places and only one point above the relegation zone.
O'Neill spent the bulk of his playing career at Nottingham Forest, where he won a European Cup winner's medal in 1980.
As a coach, he managed Wycombe Wanderers, Norwich, Leicester, Celtic and Aston Villa before switching to Sunderland.
Saturday's defeat meant Sunderland have now gone eight games without a win.
"There is a determination among the players that we can do it. And I'm as buoyant as I've always been," said O'Neill in the immediate aftermath of the loss.
He becomes the fifth top-flight manager to lose his job this season following the sackings of Roberto Di Matteo at Chelsea, Mark Hughes at Queens Park Rangers, Nigel Adkins from Southampton and Reading's Brian McDermott.
O'Neill's sacking, with just seven games remaining in the Premier League season, left observers stunned.
"Surprised Martin O'Neill has been sacked despite their recent run of results. Starting to get tight at the bottom after Wigan's win," tweeted former England striker Michael Owen.