The tackle which broke Manchester United left-back Luke Shaw's leg should have been punished, believes Uefa referees' chief Pierluigi Collina.
Referee Nicola Rizzoli took no action over the challenge by PSV Eindoven's Hector Moreno on Shaw, 20, last month.
"We certainly reminded our referees to be very, very careful with this matter," Collina said.
"Nobody reacted because what was perceived, even by players on the field of play, was the ball was played."
Italian Collina, widely regarded as football's top official before retiring in 2005, added: "This is the thought of many: if the ball is played, it is not even a foul.
"We need to make people aware that if you want to protect the safety of the player, even challenges on the ball but risky in terms of endangering safety of an opponent can be punished, should be punished."
Once play got back under way, Moreno went on to score as PSV came from behind to beat Manchester United 2-1 in the Champions League Group B encounter.
The Mexico defender later apologised after Shaw suffered a broken tibia and fibula which has left him a doubt for Euro 2016, which starts in June.
When Arsenal midfielder Aaron Ramsey suffered a similar injury against Stoke in 2010, he was ruled out for nine months.
Collina added players also had a responsibility to "be careful" when making challenges.
"We would like to convince them that getting the football is not everything," he said.
"If a player hits the ball and then endangers the opponent, he is convinced that the job was done correctly."