A number of Glentoran fans staged a car park protest against Mick McDermott after Saturday's 1-0 defeat to Larne.
The Glens crashed to their fifth successive Premiership loss as their title aspirations suffered another massive blow on Mersey Street.
Lee Bonis delivered the latest body blow, the Larne striker scoring the only goal of the game in the 64th minute.
Read more: Irish Premiership recap as Larne beat Glens and Linfield romp to victory
It leaves the Glens labouring in sixth spot in the Premiership table, 14 points behind leaders Cliftonville albeit with three games in hand.
Niall McGinn made his debut while Shay McCartan returned from a seven-game suspension, but it couldn't lift Glentoran to a much-needed win.
Chants of 'Out, Out, Out!' could be heard at the final whistle, and after the game a number of fans congregated outside the players' entrance, chanting 'Mick McDermott, get out of our club'.
A sizeable police presence was also in attendance at the ground.
It has been a seismic shift in mood at the Oval following what was a hugely positive start to the season.
Glentoran were unbeaten in their opening 11 league games, conceding just two goals in the process.
A 2-1 defeat to Glenavon in October kick-started the malaise which McDermott and his players have yet to recover from, bursting fans' dreams of lifting a first Gibson Cup since 2009.
They have recorded just one win in their last seven games across all competitions, a 2-0 victory over Moyola Park in the Irish Cup last weekend.
McDermott also came under fire for comments made after that game, labelling a small number of supporters who allegedly shouted abuse at him as "balloons".
Glentoran return to Premiership action next Friday night when they travel to Newry City.
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