Still, Heidi's dad, Bill Montag, tells UsMagazine.com he doesn't think Spencer, 26, is a bad influence on his daughter, 23.
"Heidi is such a strong-willed individual that I don't think that Spencer is going to manipulate her," he says. "Also I think she knows, and so does Spencer: if I thought my daughter was in any harm's way with Spencer, I would be there."
PHOTOS: How The Hills stars have changed
Still, he's "very worried" about Heidi, who ceased communication with her father, 63, in March and changed her phone number "so I can't even reach her," he says.
"I think that they'll realize... there are people that love them and care for them and friends and family," he says. "I pray for them to find peace and happiness. They're not going to find it in crystals and light and all this stuff I've read about."
The Colorado rancher -- who divorced Heidi's mom, Darlene Egelhoff, when Heidi was 3 -- has mixed feelings about his daughter's 10 plastic surgery procedures.
PHOTOS: Spencer and Heidi's drama-filled wedding
"Heidi always looked like me, and [her sister] Holly looks like her mom," Montag jokes. "I remember Heidi saying in a magazine once that she didn't want my nose, so I gave her grief!"
Montag says he feels like he "let her down" because he wasn't aware she was unhappy enough to change her appearance so drastically.
But he says he he stands behind his daughter's decision to alter her looks.
"We don't always approve of everything our children do, but we support them and we're there for them," he says. "She doesn't need a lecture about the whole thing. I'm not sure she's 100 percent happy with what she did or not. I don't know. But the only thing I can say is we're there and we're her family. She and I were very close before this whole thing happened."
VIDEO: Heidi struggles to eat burger because of surgery
Montag wants to see his daughter again.
"Hopefully they won't call the police on me!" he says.
Meanwhile, the Pratts are also giving the silent treatment to another relative: Spencer's grandma, "Nana," who made frequent appearances during The Hills' fourth season.
"They would send a limo and treat her like a queen," Montag says. "Now, they're not there at all."
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I wish they all would zip it!