Jesualdo Ferreira has resigned as Panathinaikos coach following a run of just two wins from their last 14 competitive matches.
That disappointing form has left Pana sixth in the Greek Super League, 15 points behind arch rivals Olympiacos, and looking set for an early exit out of Europe.
After being knocked out of the UEFA Champions League play-offs by Malaga, Pana have also struggled in the UEFA Europa League, where they currently prop up Group J with two points from four games. Lazio are top with eight points while second-placed Tottenham have six.
Portuguese Ferreira, 66, took charge of Pana in 2010 having previously been coach of numerous sides, including Porto, Malaga and Benfica.
Pana confirmed on their website that former midfielder Juan Ramon Rocha, the club's Under-20 coach who has also coached the senior side in two previous spells, has been put in charge ahead of this weekend's league game against PAOK.
"Panathinaikos has entered a critical period and we need everyone now: Administrators, players, fans and generally anyone who can help," said Rocha.
"I am always available to the Association and for that reason I come to assist in this difficult time."