What happens if you declare interest for your opponent's key player?

As it says what happens if you declare interest for your opponent's key player just before the match. Does it confuse the key player; so he would have a bad game. Or does it motivate him to show his abilities to you? Or does it **** him off, so he would play even better?

Also can you repeadetly do this; if the outcome is good for the team

You might upset your current players.

In my experience, declaring interest never caused the opposition player having a bad game.

But press conference have some effects (telling that he is a threat or the opposite, you don't worry about him); positive or negative, depending on some mental stats I guess. Making him more determined or losing concentration.