An MC at AML might have adverse affects. If you're playing them at a position they could learn (e.g. MC at ML or MC at AMC) then it seems ok. Morale is affected, but not as much as being carded or having a top player in a reserve slot. I've played an MC at AMC most of the season with superb results (one 6, four 7s, four 8s and five 9s over 14 games shown in stats) I was going to train the other position, but why waste the 50 points?