Second baseman Jason Kipnis and outfielder Albert Almora Jr. are also out with an illness.
"I don't know if I started all this crap," said Ross, who missed several days early in spring training with the flu. "Yeah, we got a couple guys banged up. We're taking precautions, especially with all the stuff that's going around, making sure to get these guys hydrated and feeling good. I know how bad personally that gets. Just be extra cautious in that area and do our best not to spread it around."
Darvish went to the hospital to get checked out, and he tweeted that he tested negative for the flu.
"My understanding is that they think it's just a daily illness," president of baseball operations Theo Epstein said.
Darvish is a leading candidate to starting Opening Day for the Cubs when they visit the Brewers on March 26, and Kipnis appears to be line for filling a big role at second base. Ross wasn't sure if this illness would affect his players in the long term at all -- specifically Darvish, who has a throwing schedule that he needs to stay on.
"I don't know yet," Ross said. "It just depends how long all these guys miss and how things line up."