That makes sense . Colo is not tough enough to play as a DM. Colo has two weaknesses: He sometimes forgets to mark his man, and he rarely tackles. He tries to win or protect the ball in the most righteous way: by standing on his feet. But that has periodically resulted in him being outmuscled leading us vulnerable for counterattacks. Sometimes you have to get dirty and tackle the ball in order to avoid such situations. And as a DM you're often attacked from both sides, while one as a defender more often than not have your back clear. Consequently, DM is probably the most physically demanding position on the pitch. That doesn't not suit Colo.
Periodically? Have a word, man. It's happened once this season - 30 PL games old, btw.