Ellis, given a scheduled game off on Friday night, said the knee that has bothered him for 10 days swelled up after he played 12 innings on Wednesday and flew cross-country on Thursday.
"The MRI came back really good," said Ellis. "There is cartilage inflammation. Smartly, against my judgment, they want me to rest another day and get ready for [Sunday]. It's been a little sore for 10 days."
Manager Don Mattingly said he didn't know of Ellis' issue until after posting Friday night's lineup, which had Matt Treanor starting at catcher. Treanor started again on Saturday. Triple-A Albuquerque catcher Tim Federowicz was pulled during Friday night's Isotopes game, just in case.
Mattingly said his emergency catcher is either Luis Cruz, who is now starting at shortstop in place of the injured Dee Gordon, or Jerry Hairston.
"Jerry told me he caught in the Cape Cod League and he was really good at it," Mattingly said with a smile. Hairston played in the Cape Cod League in 1996.
"He's Jerry Hairston, darn it, he can do anything."