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And Appiah believes there is a lot more to Portugal than just nullifying Ronaldo's influence.
"He's the best player in the whole world - everyone recognises that," he said. "You can only stop Cristiano Ronaldo, the best player in the world, by working as a team. We can't let him show what he can do.
"But it's about teamwork, I don't believe in the individual.”
Portugal's last-gasp 2-2 draw against the United States on Sunday kept their slim qualification hopes alive and set-up an important clash with Ghana in Brasilia.
With unbeaten pair Germany and USA set to do battle, Ghana must defeat Portugal and hope for a favourable result in Recife.
"It's important that we don't allow Ronaldo to play his game," Appiah continued. "We will study their game, but it's not only him, it's the whole team.
"It won't be easy to reach the round of 16 because we've only got one point. It'll be tough, it is possible."