Hudgens and the "Baywatch" actor, 29, dated from 2005 to 2010 after meeting on set of the Disney's "High School Musical," reported Us magazine.
"No... That's not a thing that happens. I completely lost contact with him," the 28-year-old actress says.
Post their split, Hudgens moved on with actor Austin Butler, who she is still dating. Efron has been romantically linked to Michelle Rodriguez, Lily Collins and ended his two-year relationship with model Sami Miro in April 2016.