UEFA refereeing chief Pierluigi Collina insisted the governing body would not allow the “mobbing” of officials.
The issue of players surrounding referees has grown as many try to influence decisions made.
Collina said managers had been reminded about mobbing referees and it would not be accepted by UEFA.
“It’s not something new the fact at a European level UEFA doesn’t allow players pressing a referee while he takes a decision,” he said.
“We won’t allow any mobbing of referees.
“Players and managers that compete in European cups know very well that UEFA doesn’t accept such behaviours and so we just reminded mangers about this aspect.”
The former referee said the image of the game was crucial, while he also warned coaches against hounding fourth officials.
“Our aim is to protect players; paying particular attention to punishing those faults that are dangerous and cause physical damage,” Collina said.
“We also want to protect the image of the game and of the competition… and for sure watching a group of players on TV pressing the referee for a decision, it’s not a nice image.
“We want to make it clear this aspect with players. We will pay particular attention to this aspect.”