ESPN reports that the complications are not believed to be serious and should have "no bearing on Rivera's ability to have surgery and return from the injury."
Rivera injured himself last week, but surgery still has not been scheduled.
"We ran into complications,'' agent Fernando Cuza told the New York Post, explaining why surgery was not scheduled. "I am referring to Dr. Ahmad and Brian Cashman for further information.''
Cashman said, according to the Post: "I won't comment on that right now."
The Yankees are still trying to gather information after Rivera met with a specialist and a team physician.