Turkish organizers also canceled the band's Thursday night concert in Istanbul.
Tuesday night's concert north of the Greek capital was canceled after Gahan, who turned 47 last week, fell ill and was hospitalized overnight. Neither organizers nor the hospital would say what he was suffering from.
But concert organizers Didi Music later issued an announcement Wednesday saying the singer was still unable to perform.
"Even though everyone hoped for the singer's speedy recovery and the rescheduling of the band's show for today ... according to the information received by the band's management and the doctor on duty, the artist's health condition does not allow it," the organizers said.
Turkish organizers also announced late Wednesday that they were canceling the band's Istanbul concert.
"Due to circumstances beyond our control, the Depeche Mode concert will not take place on May 14," the organizers, Purple Concerts, said in a statement on their Web site.
Purple Concerts was not immediately reachable, but Turkey's Anatolia news agency said Gahan would go to the United States for treatment and that concerts in Bucharest, Romania, on Saturday and Sofia, Bulgaria, next Monday might also be canceled.
The band's publicists in London gave no information on whether any other dates on Depeche Mode's tour would be affected. After Bulgaria, the band is scheduled to play in Belgrade, Serbia, next Wednesday, followed by concerts in Croatia and Poland. Depeche Mode arrived in Greece after playing in Tel Aviv, Israel, on Sunday.
The British band emerged in the early 1980s, releasing 46 singles and a dozen albums.
(This version CORRECTS to say Gahan turned 47 last week, sted last month.)
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