The battle between England right back Walker and France's top scorer Mbappe could be key to the outcome of the first encounter between the teams in the knockout phase of a major tournament.
While Walker discussed the topic at length on Wednesday, Mbappe has stayed silent.
"If he knows how to stop Kylian, good for him," Fofana told a news conference on Thursday.
"But 19 other teams in Ligue 1, and others in the Champions League, have been waiting for the solution. The truth will come from the pitch. We have full confidence in Kylian.
"Kylian does not read the papers, sorry for you! He doesn't read what you write, he focuses on his game. He is focused on what the team has to do and what he has to do. I feel he is very calm and determined."
Fofana was among the fringe players who featured for France in their last Group D game against Tunisia, which ended in a 1-0 defeat.
That result led to some comments that France lacked strength in depth, while England can rely on an impressive bench.
"Everyone is entitled to their opinion. It will be up to us to prove them wrong," said Fofana.
The winner of Saturday's clash at Al Bayt Stadium will take on either Morocco or Portugal for a place in the December 18 final.
"The team who will make fewer mistakes will win that game," France centre back Dayot Upamecano (24) predicted.
