The 37-year-old actor discussed his friendship with the 19-year-old aspiring actress on Monday's episode of the WTF with Marc Maron podcast.
"I'm close with Paris," Culkin confirmed before telling host Marc Maron he keeps his relationship with Paris, the daughter of late singer Michael Jackson, private.
"I'm going to warn you now that I am very protective of her so just look out," he said. "I'm a very open book when it comes to things but like with her, she is beloved by me."
Culkin said he keeps quiet about Paris because of his "love" for the star.
"I'm just letting you know if we want to start going down that road it's going to be a dead end you know, but I mean that in the fact that I love her so much," he said before telling Maron the teenager is doing well. "She's tall and beautiful and smart. It's great."
Culkin was a friend of Michael's, and is the godfather of Paris and her two brothers, 20-year-old Prince Jackson and 15-year-old Blanket Jackson. Paris dedicated an Instagram post to the Home Alone star on his 37th birthday in August.
"HAPPY BURFDAY I LOVE YOU," she wrote.