Scherzinger, 37, who split from Formula One driver Lewis Hamilton earlier this year, was pictured kissing the 23-year-old Olympiacos soccer star, reported The Daily Mirror.
"Nicole is on a girls' holiday celebrating her birthday. He is a friend of a friend who was in Mykonos as well," a source said, insisting "they're just friends."
While the "Poison" hitmaker was seen having fun with the soccer star, the source said she and Lewis are still "friends".
The racing driver took to Instagram to send a heartfelt birthday message to the singer.
"I'm wishing you the Happiest of Birthdays, and may God continue to Bless you in all that you do," he said.