The duo was spotted together enjoying lunch at Taco Beach Shack in Hollywood, Fla., on Monday, an onlooker tells PEOPLE.
"Hayden had two grilled mahi mahi tacos and a margarita while Wladimir had six mahi mahi tacos and a coke," the source says.
After lunch, the Nashville star – who was dressed casually – removed her brown leather jacket to play table tennis on the restaurant's ping pong table.
Champion boxer Klitschko gave Panettiere a few pointers and "wrapped his arms around her from behind to show her his own style of hand and eye coordination," the source adds.
As the pair exited the restaurant, a generous Klitschko left a "$20 tip on a $20 tab."
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