Manchester United manager Sir Alex Ferguson says players who feign injury in order to get play stopped are 'killing' the game.
The Red Devils tactician remains unhappy Chelsea players failed to kick the ball out of play in the Community Shield at Wembley when Patrice Evra was down injured.
The Blues went on to score with United's left-back injured while, in the same game, Michael Ballack stayed down for the game to be stopped only to spring to his feet once the whistle was blown.
Ferguson believes the players and not referees should be more professional and that The Football Association needs to act now in order to clear up the unwritten rule about kicking the ball out of play.
The experienced Scottish tactician has told his players to try to continue playing whenever possible and to let the referee decide if play should be stopped - something they have struggled to grasp.
"This unwritten rule has come into the game and opportunist players have just overdone it. They have overcooked the whole thing," he said.
"Last week, Evra was through and into the last third of the pitch, the referee stops it and (Michael) Ballack gets up. It could have been a serious problem so he stopped the game.
"Then when Evra is fouled, Chelsea don't kick the ball out, the referee plays on and we lose a goal. It is a grey area and something has to be done about it.
"The players are killing the game. The players' unprofessionalism is killing the game. Not the referees. The problem is how much the referee can tolerate when the players lie down pretending to be injured.
"There is no doubt that this unwritten rule about players kicking the ball into touch has been exploited to ridiculous degrees now."
Ferguson added: "I spoke to my players about it and told them not to kick the ball out, that they should let the referee decide when to stop the game.
"But the players wouldn't do it. If players don't put the ball out they get stick off opposing players and opposing fans.
"If a referee stops the game twice when players go down and on the third occasion he decides to play on, he makes a rod for his own back.
"Last Sunday, Chelsea had plenty of time to kick the ball out when Patrice Evra was injured after being fouled by Michael Ballack."