The couple first started dating in 2009 but split up in 2011. They got back together earlier this year after the actress split with her boyfriend Scotty McKnight.
According to UsMagazine.com, Panettiere, 23, and the Ukranian athlete, 37, are thinking about having a summer wedding.
A source told the website: "Very few people know, and she isn't wearing her ring publicly yet."
Panettiere is known for her role on the NBC superhero drama "Heroes" as well as her work in films such as "Racing Stripes," "I Love You Beth Cooper," and "Scream 4."