Tony Pulis has been sacked as West Brom head coach with the club a point above the Premier League relegation zone and without a win in 10 top-flight games.
The Baggies were beaten 4-0 at home by Chelsea on Saturday.
Albion won their first three games of the season, but have drawn four and lost seven since beating Accrington in the Carabao Cup on August 22.
Former West Brom manager Gary Megson, who had been Pulis’ assistant, is taking over “until further notice”.
Welshman Pulis said he was “proud” to have managed the club and predicted the team can finish in the “upper reaches” of the table.
“My remit was to develop the squad and ensure we delivered results which would in turn improve the club’s financial position,” he said.
“We have achieved this year on year and I am pleased to have played a part in the club’s growth.
“This season, expectations have risen and although we are disappointed with some of our results, one thing I would never question is this group’s work ethic and application.”
Pulis has been linked with the Wales manager’s job vacated by Chris Coleman on Friday.
Chairman John Williams said: “These decisions are never taken lightly but always in the interests of the club.
“We are in a results business and over the back end of last season and this season to date, ours have been very disappointing.
“We would like to place on record our appreciation of Tony’s contribution and hard work during a period of transition for the club which included a change of ownership. We wish him well in his future endeavours.”
West Brom faces Tottenham in the Premier League at Wembley on Saturday, and follow that with home games against Newcastle (November 28) and Crystal Palace (December 2).