Brazil coach Dunga said 15 of his players dealt with a virus in the week leading up to their defeat to Paraguay in the Copa America semifinals on Saturday.
Paraguay eliminated Brazil at the quarterfinal stage for the second straight tournament by winning 4-3 on penalties after the 90 minutes ended 1-1.
Dunga said Brazil could not train the way they would have like before the game, but refused to blame the defeat on the illness.
"It's not an excuse, but 15 of our players suffered from a virus this week. We had to limit some training sessions," Dunga said in his post-match press conference.
"Players suffered from a lot of headaches, back pain and illness -- some felt it more than others. We had to reduce the intensity of training to try and help them recover. Some of them were vomiting.
Some of the players even weren't feeling well during the game, Dunga said.
"Willian wasn't feeling well at half-time, and Robinho was suffering in the end."
Rather than the virus, Dunga pinned the loss on a lack of attacking speed.
"We had to balance the match on the physical aspect, and tried to win until the very end," Dunga said.
"We tried to neutralise their main game-plan -- the aerial ball. We had good moments through the match, with speed and switching between the sides.
"Today we had an important match that needed speed and we lacked that in the end."
Brazil were also without star forward Neymar, who was suspended after earning a red card in the second group-stage match against Colombia.
"Historically the Copa America is very complicated. Brazil won a few times, but when you win nothing is said. And when you lose we always say that something is missing," Dunga concluded.
"We lost five players for this year's tournament, and that makes it harder. There is a renovation for us to do, but we can't put aside the experience gathered on a tournament like this.
"Neymar is important, like he is important for Barcelona, but we have quality players.
"We wished we could win, it was a great lesson, but the World Cup qualifiers are still our greatest goal."