Peru coach Ricardo Gareca said Jefferson Farfan played with "an allergy" during his team's 2-1 loss to Brazil at the Copa America on Sunday.
It was speculated in the lead-up that Farfan, 30, would miss the clash in Temuco, but he started and played 83 minutes.
Neymar inspired Brazil's win, which came thanks to a 92nd-minute goal from substitute Douglas Costa.
Gareca confirmed Farfan had played in discomfort, and he wants to keep his players fresh ahead of their final two Group C games.
"Farfan has being suffering with an allergy and he is under treatment," he said.
"He was in doubt until the beginning of the game but later we probed him and he responded well but he still has some problems so he made a great effort.
"We asked him about his condition when he was done everything that we have asked for.
"With [Juan Manuel] Vargas, he asked to be substituted and we did.
"The idea is to maintain the players in the best way possible because this doesn't end here.
"Independently it was important to get a good result in the first game, we still have two finals in front and we need our players in form that's why we made the changes."
Gareca praised Christian Cueva, who opened the scoring in the third minute for Peru.
Neymar equalised just two minutes later before the Barcelona star set up Costa for the match-winner.
"He made a great game. Cueva played well in the right wing he is adapting to a position we think he can handle very well," Gareca said.
"He is progressing in every game and that's important for us."
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