"He's got a virus that attacked his liver, so he's seen an infectious disease (specialist) today and we should know more here in the next little bit. I don't know how long he's going to be out," Blashill said, according to MLive's Ansar Khan.
Green had surgery in April for a herniated disc but his current ailment is unrelated, according to general manager Ken Holland.
"The day before camp he saw the doctor in New York on his neck, he was totally cleared, cleared for contact," Holland said. "The plan was to ramp him up and play him the two of the last three preseason games. As we got into camp and were on the ice two, three, four days he didn't feel like he had his energy, he felt a little bit fatigued. Our doctors did some initial bloodwork, and now we're trying to get him to see a doctor today or Monday gather more information."
Green signed a two-year, $10.75-million contract in July to stick with the Red Wings. Last season, the 32-year-old recorded eight goals and 25 assists in 66 games.