https://www.pcgamer.com/leaked-image-indicates-assassins-creed-odyssey-will-be-set-in-ancient-greece/

A rumor surfaced in March on Comicbook.com indicating that the next Assassin's Creed game will be set in ancient Greece. "Several sources" said it was so, although the site advised approaching the story with all appropriate caution; but it also noted that "murmurs" of a possible Greek setting had previously come up earlier in the development of Assassin's Creed: Origins.   

French gaming site JeuxVideo added weight to that story today, and also a possible title, with an image of an Assassin's Creed: Odyssey "collectible helmet keychain." The helmet is very clearly in the Greek style, and the Odyssey is a famed epic about the Greek hero Odysseus, who takes the long way home after the Trojan War. That could make the Assassin's Creed timeline a bit hinky—Ptolemaic Egypt, the setting for Origins, didn't come into being until nearly a millennium after the Trojan War—but it's also possible that "Odyssey" isn't a specific reference to the poem as it is a cool word that very loosely fits the motif.