The 29-year-old is with the Ivory Coast squad preparing for the Africa Cup of Nations and was laid low with a flu-like virus.
But his brother and City team-mate Kolo allayed fears that his health was in any serious jeopardy, telling the club's official website: "Yaya had a couple of days off.
"He is back on his feet now. It was just a short illness, sort of like flu. Apart from that, everything is going very well at the training camp and we are happy to be here."
The Ivorians are seeking to banish the painful memory of penalty shoot-out defeat to Zambia in last year's final, and begin their campaign against Togo on January 22.