Does he get scared

Yes.
As scared as SAF will be when we come to old trafford :)

Hes not a big game player. the only time l remeber him playing well in a big game was the champions league final, other than that he has been average. (even in the champions league final he faded after he scored)

l do not know is he flops in big games as you believe

he is not as dangerous as he is in the EPL games

who knows, maybe that is kind of his weakness, every player has one. for Messi, it is the fact that he really is not good at headers, or when the ball is in the air, he loves it on the ground. l guess one of CR7 is weakness is that he gets a whole lot of pressure before big games and flops them.
he is still a great player though (even though l do not like him.)

Look l am not his biggest admirer but often in ''big'' games he is swamped with attention with sometimes 2 or 3 players designated to mark him & also he gets chopped a fair bit. Yes before u say it, he goes down easy at times too. l think in those games he sometimes backs off because he knows he will not have the impact required. Yes sometimes he gets petulant & sulks when something does not go his way & just takes himself out of the game as well. l acknowledge that. But look the same could be said of Gerrard playing for England. Why does he disappear & at times not show up at all. You'd really have to ask the players themselves.