His comments came hours after Zubik, leader of Pennsylvania's second-largest Catholic community, took the unusual step of calling a news conference to disclose the allegation and deny it.
According to Zubik, his accuser claimed he forced him up against a wall in the school chapel and tried to kiss him when both were at Quigley Catholic High School in Baden a quarter-century ago.
"I emphatically state no such behavior occurred, nor any semblance of such behavior," Zubik said. "The accusation is false, offensive, and outrageous."
Rock could not be reached for comment.
Zubik, 62, was named bishop of Pittsburgh in 2007, after holding the same post in Green Bay, Wis.
During his news conference, Zubik said he had known of the allegation since August and that someone had briefly posted it online. He said it was a relief to be able to disclose it.
"Take a look at this collar," Zubik said. "I've been putting this collar on every day for the past 40 years. In the name of my brother priests, I want to say this collar is not a bull's-eye. All I can do is come before everybody and hope that people will believe what I say is true."
Berosh said that Rock had leveled similar allegations earlier this summer against a defrocked priest, but that the statute of limitations for prosecuting that case had expired.
Days after Rock was rejected for a lay position within his own parish, he made the new abuse allegations in an e-mail to the diocese, according to Berosh. In addition to his claim against Zubik, he claimed to have been fondled by a nun on a plane and assaulted by another priest.
But investigators were skeptical because Rock was initially reluctant to cooperate. When he did, Berosh said, he gave "twisted and convoluted facts."
Contact staff writer John P. Martin at 215-854-4774, firstname.lastname@example.org, or @JPmartinInky on Twitter.