Earlier, the government had said Foreign Minister Dimitris Avramopoulos would go in place of Prime Minister Antonis Samaras. But on Monday, it was announced that President Karolos Papoulias, 83, will head the delegation to Brussels instead.
The reason for the change was to comply with EU regulations according to which a head of state must lead the delegation.
The presidency in Greece is a largely ceremonial post.
Samaras, who took over as premier last week, was discharged from hospital Monday, two days after undergoing eye surgery.
His doctors have said he must stay home to recover for several days and cannot travel. The summit is Thursday and Friday.