Modern Greek?
In terms of vocabulary, Italian (including Venetian), but not by much; toss-up between Italian and Turkish. Then Latin, then French, then English.
In terms of grammar, any significant influence was through the Balkan Sprachbund. A lot of the Sprachbund features originated in Greek (and we can tell through the history of Greek and Old Church Slavonic); but not all of it. It’s very hard to disentangle Albanian and Macedonian–Bulgarian as influences, so I won’t.