Chelsea manager Luiz Felipe Scolari admits Cristiano Ronaldo deserves to be crowned the world's best player but he has warned the Manchester United winger he could lose the title in 2009.

Ronaldo is favourite to collect the FIFA World Player of the Year award for 2008 when it is presented in Zurich on Monday.

The Portugal star, who is nominated alongside Liverpool striker Fernando Torres, AC Milan playmaker Kaka and Barcelona duo Lionel Messi and Xavi, has already won the European honour and Scolari is convinced his superb form for United last season deserves another reward.

But the Brazilian knows Ronaldo better than most after coaching him with the Portugal national team for five years and he hinted that the United idol has been below par so far this season.

"In the last season, for me, he was the best in the world. If he doesn't receive the award it will be wrong," Scolari said.

"He is a very intelligent player that changes games. When you expect him to be on the left, he turns up on the right. When you expect him to shoot with his left, he shoots with his right. But this season maybe some other players are in a good position to discuss it," the former Portugal manager added.

Ronaldo scored 42 goals to help United win the Premier League and Champions League last season, but he spent most of the close season unsuccessfully trying to engineer a move to Real Madrid and has cut a forlorn figure at times since then.

The 23-year-old has scored just nine times and has failed to hit the net in his last eight appearances, yet he could easily prove Scolari wrong by helping United to a crucial win over Chelsea at Old Trafford on Sunday.

He only made a cameo appearance as a substitute in the 1-1 draw between the teams at Stamford Bridge earlier this season. Now the stage is set for a more significant contribution.

Scolari knows none of his Chelsea players have Ronaldo's flamboyant skills but he believes the likes of Deco, Frank Lampard, Michael Ballack and Joe Cole are just as capable of winning a match on their own.

"I have some players who don't have his characteristics but I have others who have fantasy," he said.

They cross very well and pass very well. This is different player with a different style. Maybe we have here with a different style but who are as good as Ronaldo. For sure, one player from Chelsea will be in the best five players in the world this year," Scolari added.