Jesualdo Ferreira has been replaced as Panathinaikos boss by scout Juan Ramon Rocha following the club's poor start to the season.
Eighth in the Greek Superleague after ten matches they also trail rivals Olympiakos by 15 points and sit rock-bottom of their Europa League group.
Ferreira, 66, resigned on Wednesday but the Greek side immediately confirmed that he was to be replaced by Rocha, 58, who previously took charge of the side between 1994-96, a spell in which he took them to the Champions League semi-finals, and spent nine years on the books as a player between 1980-89.
Upon his reappointment Rocha underlined the seriousness of the situation the club find themselves in, stressing the need for everyone to be united in the cause.
"Panathinaikos has entered into a critical period and we need everyone to be united from the administration, to the players and the fans, as well as generally anyone who can help," he said.
Ferreira accepted his share of the blame for Panathinaikos' recent failings, but also pointed to enemies in the media for exaggerating the problems within the 20-time Greek champions.
"Mistakes were made, also on my part, but the possibilities for improvements were limited," he said.
"I had to deal with enemies in the press who decided to magnify the complaints of fans making my task even more difficult, and this climate created by those people had a negative effect on the players.
"It got to the point where I felt that I was more of a problem for Panathinaikos and not the person to solve the problems, as I was last season, and for all of these reasons I decided to resign."