Nani has said he is looking forward to facing "special" Barcelona star Lionel Messi at the Mestalla on Saturday.
But Marca reported the Valencia winger as saying his Portugal international captain Cristiano Ronaldo would provide tough competition in the race for the Ballon d'Or.
Messi scored a hat trick as Barcelona swept past Manchester City 4-0 in the Champions League on Wednesday -- his fourth goal in two games since returning from injury.
And Nani said: "Messi is a special player and there are very few who can compare with him.
"But I know that Cristiano will fight hard with him all year for the Ballon d'Or.
"Messi is going through a great time at the moment, but things aren't decided yet -- and you won't know until the end of the year who is the best in the world."
Valencia have won three of their past four league matches and former Manchester United star Nani said he believed they could cause problems for Barcelona, who are fourth in the early La Liga table.
"We have good players and a united team, so that means that anything can happen," he said.
"We have to be clinical. We know that we will have to make the most of the chances that come our way because we are fully aware that we won't get many."