According to Gordon Wittenmyer of the Chicago Sun-Times, Darvish tweeted in Japanese that he went to hospital because he had been coughing since Wednesday and "couldn't be certain" he hadn't contracted the coronavirus.
On Tuesday, the Japan native told Wittenmyer that he was "really worried about" the coronavirus and its spread.
According to CNN, more than 95,000 cases of COVID-19 have been reported worldwide, with over 3,300 deaths as a result.
Asia has been hit hardest by the coronavirus, with more infected patients being reported in China than any other country. At least 163 cases of the new virus have been reported in the United States thus far, and there have been 11 reported deaths.
Per Wittenmyer, several teams have dealt with the flu during spring training, including the Cubs. Starting pitcher Jose Quintana, second baseman Jason Kipnis and manager David Ross are among those who have been impacted.
The 33-year-old Darvish is expected to be a key part of the Cubs' rotation in 2020 after going 6-8 with a 3.98 ERA and 229 strikeouts in 178.2 innings over 31 starts last season.
It marked a significant bounce back for the four-time All-Star, as he struggled to a 4.95 ERA in his first campaign with the Cubs in 2018 and was limited to just eight appearances because of injury.
With Darvish, Jon Lester, Kyle Hendricks and Quintana, the Cubs could have one of the best rotations in baseball and figure to be a factor in the National League Central.