The designated hitter told the New York Post that he tested positive for Epstein-Barr virus, most commonly associated with mononucleosis. Holliday, 37, first started experiencing symptoms in Oakland on June 17. He was initially thought to have suffered an allergic reaction to something he ate.
After missing a game, he returned to start in six contests. But weakened and playing through body aches, he batted just 4-for-22.
Holliday, who last played June 24, was then placed on the 10-day disabled list.
According to the Centers for Disease Control and Prevention, Epstein-Barr is one of the most common human viruses in the world and is spread most commonly through bodily fluids, primarily saliva. Most people contract the virus at some point of their lives but not have any symptoms. EBV also has been linked to certain cancers.
Holliday participated in batting practice before Wednesday's game against the Blue Jay, sending several balls into the left-field stands, the Post reported.
"I've been feeling much better,'' he told the newspaper.
Holliday added that he doesn't believe he'll need a minor-league rehab assignment because he'll only have been out of action about two weeks.
Holliday, who signed a one-year, $13 million contract with the Yankees in December after spending the previous seven-plus years with the Cardinals, is hitting .262 with 15 home runs and 47 RBIs.
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