"There's been some unforeseen things that we've had to navigate around, which is really unfortunate, in the sense of health," said Johnson.
"It's not an excuse, because we have depth, but I'll just say I'm grateful we have a team doctor."
Johnson, who has made five Ryder Cup appearances as a player and served as vice-captain three times, did not reveal too much about the illness but said it passed around between the caddies and players.
The U.S. won the 2021 Ryder Cup at home in dominant fashion but now have a mountain to climb if they hope to end a 30-year drought on European soil this weekend.
Johnson, who raised some eyebrows for not playing Jordan Spieth, Justin Thomas and Brooks Koepka in the morning session and also for sending out two Ryder Cup rookie pairings, said the illness affected some of his lineup decisions.
Persons:
Zach Johnson, Johnson, There's, we've, Jordan Spieth, Justin Thomas, Brooks Koepka, Frank Pingue, Ken Ferris
Organizations:
Ryder, Europe, U.S, Thomson
Locations:
Europe, Toronto