Los Angeles prosecutors said on Wednesday that their sex crimes team was reviewing a case against Sylvester Stallone.
Greg Risling, spokesman for the Los Angeles District Attorney's office, did not give any further details but said the case was presented by police in Santa Monica, California.
"My client categorically denies the allegations," Stallone's attorney, Martin Singer, told CNN.
"It's outrageous that the DA's office and PD would announce this information because it makes the public think that there's something there."
Singer said the woman who made the complaint had a consensual relationship with his client in the 1980s. "It's not appropriate to try to ruin someone by doing this," he added.
Santa Monica police said in December they were investigating a complaint that was made in November 2017 regarding an alleged incident of sexual misconduct in the 1990s by the actor.
Stallone skyrocketed to fame in 1976 with his Oscar-winning boxing film Rocky and went on to become one of Hollywood's biggest action stars.
California has a complex statute of limitations for criminal prosecutions of sexual abuse but offences must generally be prosecuted within 10 years.