Should George Papandreou step down, the man widely tipped to take over the role as Greek PM, at least temporarily, would be the Finance Minister Evangelos Venizelos.
Divisions with Papandreou became immediately apparent last Monday when the PM announced his intention to hold a referendum on the euro zone bailout plan.
Venizelos had not been told of the plan and strongly opposed the idea.
Nevertheless it was he who saved the party in the confidence vote by persuading deputies to back Papandreou, on condition that the PM would form a coalition government and step down.
If that happens it is thought Venizelos will step in and lead the coalition to elections in February next year.