Ferguson said: "I am worried too many defenders are pursuing a policy of stopping Ronaldo by fair means or foul.

"Some of the tackles on him have been ridiculous this season.

"I don't mean defenders should let him through, but I do expect refs to protect him more.

"I expect opposition fans to boo our man but I don't expect refs to be influenced by the hostility.

"Special players like Ronaldo, whom fans want to see play, need to be encouraged rather than kicked out of the game."