The midfielder is a booking away from suspension for their clash with Liverpool.
"Through experience you realise that when you've got something in your head, normally it goes against you. He needs to be normal and natural with his way of play and that will allow him to be himself," said Martinez.
"James McCarthy isn't a player that gets bookings in his normal way of playing. Last year he played every single game and in 38 games he was never (banned) with a yellow card.
"It's a situation where he's come to a new club and been adjusting and adapting and getting to know the players around him and that's probably why he's got the number of bookings that he has."
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