Jackson died June 25, leaving behind three children -- 12-year-old Prince Michael, 11-year-old Paris and 7-year-old Prince Michael II, whose nickname reportedly is Blanket.
Culkin, 29, is a former child star who at one time had been close friends with Jackson.
Britain's The Sun newspaper reported the "Home Alone" actor had donated the sperm to father Prince Michael II.
"The inquiries are too preposterous for us to even acknowledge," Culkin's representative Michelle Bega told TMZ when contacted for a comment on The Sun report.
Swim Week Miami Beach 2014 [PHOTOS]