Greece's governing coalition has again failed to agree on how to resume transmissions by state broadcaster ERT, shut down by the government last week.
Evangelos Venizelos, leader of junior partner Pasok, said there was now "an issue regarding the very existence... of the government".
PM Antonis Samaras wants to replace ERT with a smaller broadcaster.
Disagreement within the coalition over the issue has raised fears that the government might collapse.
'No common ground'
The third coalition partner, Democratic Left, said it would probably pull out of the government, though it would back certain bills in parliament.
Further talks are going on behind closed doors, with an announcement expected later on Friday.
Withdrawal would mean a government majority of just three in parliament. That would fuel fears of political instability hampering Greece's ability to manage its debt crisis, the BBC's Mark Lowen reports from Athens.
Prime Minister Samaras says Greece will not slide into fresh elections and that his government will remain for another three years.
But without the Democratic Left, the coalition will be seen as far less representative, our correspondent says. Mr Samaras's conservative New Democracy and the socialist Pasok have alternated in power for the last four decades and are widely blamed for leading Greece into financial disaster.
On Monday Greece's top administrative court ordered that ERT could resume transmissions.
However, correspondents say there have been varying interpretations of the ruling by the court, the Council of State.
Mr Venizelos and Democratic Left leader Fotis Kouvelis want public broadcasts to be restored.
After the talks broke up on Thursday, Mr Venizelos said the situation was now "particularly crucial", adding: "There is an issue regarding the very existence and prospects of the government."
Mr Kouvelis said there had been "no common political ground".
Mr Samaras shut down ERT describing it as "a case of an exceptional lack of transparency and incredible extravagance".
However, the two junior coalition partners were furious that they had not been consulted.
The move also triggered protests across the country.
ERT's audience share in 2013 was relatively low, at below 20%, with most Greeks preferring commercial broadcasters. Its cost and efficiency have long been questioned since its ratings fell in the mid-1990s.
The Council of State upheld Mr Samaras's plan to replace ERT with a smaller broadcaster, but said it should resume transmissions in the meantime.
Despite the ruling the station remains off-air.