PASOK leader Evangelos Venizelos is due to meet his conservative counterpart Antonis Samaras on Friday in an attempt to form a unity government.
Venizelos is the third party leader to try to form a coalition after Sunday's election produced a hung parliament.
The two men are scheduled to meet at 10 a.m. Venizelos, whose socialist party finished third in the vote, is due to meet with Alexis Tsipras, leader of the SYRIZA left-wing coalition, at 1 p.m.
The meetings take place a day after Democratic Left leader Fotis Kouvelis backed the formation of an ecumenical administration.
Kouvelis had previously insisted he would not enter a coalition with ND and PASOK as long as the two parties remained committed to the austerity policies applied over the last two years.
The Democratic Left chief appeared to believe that a unity government with a specific agenda could meet his two specific goals of keeping Greece in the euro and moving the country away from the fiscal restrictions of the program agreed with the European Union and International Monetary Fund.
Speaking on Skai TV on Friday, Kouvelis stressed that a national unity government has to include SYRIZA, the surprise package of May 6 election that pushed PASOK into third place.