Also, pitcher Kyle Hendricks was scratched from Tuesday's start vs. Milwaukee "out of an abundance of caution" after the right-hander wasn't feeling well, the team said.
Cubs manager David Ross said none of the players tested positive, but the team is being careful considering the condition of the coaches.
"If you have a headache, if you have a runny nose, if you have body aches, if you have just about anything going on that would or could be one of the COVID symptoms, we're going to err on the side of caution," he said Tuesday afternoon.
The Cubs had zero positive tests in 2020 but haven't had the same luck this season. Driver tested positive last week, while Young received his positive test result on Monday morning, forcing the three relievers to go on the list that day as well.
"Driver had one shot of the vaccine when he tested positive, but Young was fully vaccinated when he caught the virus. It's believed he contracted it before his second shot," Ross explained.
It's assumed the three relievers were in close contact with Young while in the bullpen, but Duffy represents the first non-pitcher to appear on the COVID-19-related injured list.
It is unknown when the players or coaches will be able to return.
The Cubs called up Ildemaro Vargas from their alternate site to take Duffy's place on the roster.
Ross indicated the change in climate as a possible reason some players aren't feeling their best.
"There's been guys that have been dealing with symptoms that we want to be cautious about," Ross reiterated.