The 42-year-old model, who split from ex-husband Seal in 2012 after seven years of marriage, is "obsessed" with Schnabel, 29, reported Female First.
"Heidi is obsessed with him. She's totally serious about marrying him. She says he's an old soul and great with the kids, so why not make it official. No one will be surprised if they're engaged soon ... Heidi has never been good at being alone," said a source close to Klum.
The German beauty declared her love for Schnabel on Instagram last month, while wishing him a happy birthday.