The extension is the latest delay in a long-running saga over permitting issues for two of Eldorado's three Kassandra projects, which prompted the miner to put its Skouries gold development on hold last month.
Greece's ministries of finance, and environment and energy, initiated the arbitration against Eldorado's Hellas Gold subsidiary in September, alleging the technical study for the plant designed to treat Olympias and Skouries concentrates was deficient.
Eldorado has maintained the study is robust and initiated legal action last month over the "unjustifiable delays" to its Skouries development.
The company holds the three 95%-owned Kassandra assets, the Skouries and Olympias gold projects and operational Stratoni lead and zinc mine, through its Hellas Gold subsidiary.
Eldorado said the extension was at the request of the arbitral panel was agreed to by Hellas and the ministries.
"The company remains confident that the current arbitration will demonstrate its adherence to all applicable laws and regulations," Eldorado said.
"The company believes that with open dialogue both parties will come to a mutually agreeable solution to enable full and efficient development of the Company's Kassandra assets in the Halkidiki region, Greece."
The Olympias development was granted overdue permits in September, days after Eldorado threatened to suspend investment in the country, and is ramping up to commercial production.
Shares in the company have headed lower since a 52-week high of C$5.13 achieved in the first half of the year and closed down 1.84% to $1.60 yesterday, a little above its 52-week low reached earlier this month of $1.39.