The Brazilian insisted he would have no hesitation staying away if he felt football's governing body had failed to address the problem.
He said: "Yaya was sad and feeling really down when we met back at the training ground in Carrington (on Thursday).
"It's unbelievable that in 2013 we still have to deal with these kinds of things. It's about time someone did something to end racism in the game, once and for all.
"I hope it doesn't come to that (a boycott), because we wouldn't want to deprive the World Cup of such a talented guy as him.
"But we need UEFA and FIFA to act, and I am quite clear in my mind. If by 2018 nothing changes, I will support the boycott."
For breaking stories and all the great banter like us on Facebook: facebook.com/tribalfootball