Ronnie McFall has resigned as Glentoran manager, the club announced on Thursday.
Former player Gary Smyth will take charge and be assisted by former club captain Paul Leeman.
Smyth and Leeman had been part of McFall's coaching team, along with Kieran Harding, since May.
McFall, who won four championships at Portadown, was appointed for a second spell as Glentoran manager in February 2018 after Gary Haveron's dismissal.
The Glens' 4-2 defeat at home to Dungannon Swifts on Tuesday was their 10th league match without a win - the worst run in the club's 137-year history.
They are five points ahead of one-from-bottom Newry City in the Irish Premiership and McFall admitted after the New Year's Day loss that the east Belfast outfit are fighting for top-flight survival.
"Gary Smyth will take responsibility for first team matters as outlined in our long term strategy. Gary will be assisted by Paul Leeman," a Glentoran club statement said.
"The Board of Directors would like to thank Ronnie for his hard work and complete commitment over the past 11 months and to wish he and his wife Anne all the very best for the future.
"Ronnie - as both player and manager - has played a very important role in the history of Glentoran Football Club. He and Anne will always be very welcome at the Oval."
The Glens are away to Crusaders in the fifth round of the Irish Cup on Saturday.
Former defender Smyth, 49, made 364 appearances for Glentoran and also had spells with Glenavon, Ballymena United and Crusaders.
He was manager of Championship club H&W Welders before joining McFall's backroom team at the Oval, along with long-time Glens team-mate Leeman.
It was expected when he and Leeman were appointed in May that Smyth would eventually assume the position of manager.