Sir Alex Ferguson fears Cristiano Ronaldo could suffer a serious injury unless referees begin to clamp down on cynical fouls against the Manchester United winger.
Ronaldo, 22, is out of Sunday's derby game against Manchester City at Eastlands after receiving a three-match ban following his red card for head-butting Portsmouth midfielder Richard Hughes during Wednesday's Premiership draw at Fratton Park.
The Portugal international was subjected to a rough treatment by Harry Redknapp's team before lashing out against Hughes in the closing stages of the game.
And although United boss Ferguson refused to defend Ronaldo for retaliating, he insisted that flair players like Ronaldo and Carlos Tevez are being let-down by officials and that the consequences are potentially serious.
Ferguson said, "It has been going on for a hundred years where the perpetrator of an incident ends up getting less punishment than the other player and Ronaldo fell into the trap at Portsmouth."
"Ronaldo will miss the City game because of it and that's very disappointing, but it was the same referee on Wednesday that sent him off against City a couple of years ago after he had been picked all over the pitch. It's a bitter experience for Cristiano."
"It seems as though referees are now more tolerant of physical contact and lots of challenges are going unpunished these days. I don't know why that's the case, but maybe referees have been told to manage situations differently."
"I always believed that it was black-and-white whereby tackles from behind were outlawed, but Ronaldo continues to be a victim and my worry is that somebody will end up getting a serious injury."
"You will never change Ronaldo, but if we continue to get weak referees like we had this week, then he is going to be suffering."
United travel to City trailing their Mancunian neighbours by four points after failing to win either of their two opening games of the season against Reading and Portsmouth.
Ferguson will still be without knee injury victim Owen Hargreaves and crocked captain Gary Neville for the game, with Wayne Rooney out with a broken foot and Ronaldo suspended.
But the Old Trafford boss insists he is confident that the champions will quickly turn the corner and get the defence of their title back on track.
He said, "We have dropped points, but the performances levels are very good and I expect the players to come right. We have the experience to do that."
"City have had a fantastic start and it has surprised me because I expected West Ham, their opponents on the opening day, to do better this season, but they were well-beaten by City."
"Although we have a lot of challenges, this is City's biggest game of the season and they want to give their fans the bragging rights in the city when they go back into work on Monday morning, so we know how big a game this is."