Man Marking (sort of player naming)

First off, im not naming the player in question, but i will be naming the opposition players some of which are very high profile it shouldnt even need a spoiler

Right, i have a DM, and he is an awesome man marker. He can mark players like Lampard, Gerrard, and any number of world class midlfielders out of a game. My question is this, his preffered position is DM (light green dot) although depending on the oppo formation i may play him at CM (dark green dot). If i employ him as a man marker in his less favoured CM (dark green) position will it affect his performance as basically his only duty is to stick to the person i assign him to? Thanks for any views/advice