UEFA's head of referees Pierluigi Collina has warned cautions will be given to players who surround officials at Euro 2012.

The Italian is preparing to put the officials who will be in charge in Poland and Ukraine through their paces in Warsaw this week.

Speaking at a news conference on Wednesday, Collina said clamping down on the mobbing of referees was a key target.

"We do not want to have referees surrounded by protesting players. This is not good for the image of the match, for the image of football," he said.

"Respect means also to the referee so players will be informed that mobbing the referee is not allowed.

"And the referee knows that if they are surrounded by players, some yellow cards - one or more - are to be expected."

The vexed issue of goal-line technology has dominated discussion before the tournament, and though it will not be used this year referee Howard Webb is open to its implementation at a later stage.

"Of course, at the moment we don't know whether the technology will come into the game ... so we'll see how that goes," Webb said.

"Whatever tools are given to me and my colleagues as referees, we'll use them to the full to enhance our performances. At the moment we don't know which way that's going to go."