"We ran into complications," Fernando Cuza told the New York Post. "I am referring to Dr. (Christopher) Ahmad and (Yankees general manager) Brian Cashman for further information."
Ahmad, of New York Presbyterian Hospital, is the Yankees' team physician.
A high-ranking team official told ESPNNewYork.com Tuesday morning that he didn't believe the complications were serious, but he said the team was still gathering information.
Another team official, who wouldn't specify Rivera's "complication," told ESPNNewYork.com that the pitcher had not suffered a torn medial collateral ligament in addition to a torn ACL and damaged meniscus -- a significant revelation because when an athlete tears all three, orthopedic surgeons refer to it as "the terrible triad" -- generally a career-ending injury scenario.
"No surgery has been scheduled yet," Cashman said. "I think (Rivera) will be here tomorrow and will be able to talk you."
Cashman declined to comment in detail when asked specifically about Cuza's comments.
"I have no comment on that," Cashman said.
Cashman said the "complications" will not impact Rivera's ability to return from the injury. ESPN The Magazine's Buster Olney earlier reported the "complications" would not affect Rivera's ability to have surgery or return to play in 2013.
"I'll let Mo talk about it when he is here," Cashman said. "Any follow-ups on that should go to Mo. He is in good spirits and you'll see him tomorrow."
Cashman did rule out any chance that Rivera could return this season.
"What he's got is correctable," Cashman said.
On Monday, Dr. Russell Warren, a knee specialist at the Hospital for Special Surgery; Dr. David Altchek, the New York Mets' team physician; and Ahmad all examined Rivera's knee.
After Rivera fell on the warning track May 3 while shagging fly balls in Kansas City, the Royals' doctors diagnosed a torn ACL and a damaged meniscus in his right knee. Rivera is expected to have surgery and has vowed that he will pitch again.
Most estimates have Rivera missing this year and returning in 2013. But Rivera hasn't ruled out a return this season.
Prior to the injury, Rivera had hinted this could be his final season. After the diagnosis, though, Rivera defiantly said he would return.
"I can't go out like this," Rivera said.
Information from ESPNNewYork.com's Wallace Matthews was included in this report.