Sounds like hes played with an illegal formation. You need 3 defenders, 1 side player on each side, 1 striker and obviously a goalie to make it legal.
i played with 3xCD,1DMC,3MC,1AML(ALSO AMC),2ST
and yes i used a MC as a DMC,but yesterday and the day before i`ve played with a MC as a DL and i won without no problem,the only difference is now i didn`t use side defenders...