The pair are shining for United's U21 team.
"Adnan is a beautifully balanced player," Sir Alex told Inside United. "He's only 18 and still to grow into his frame. But he has good balance, good acceleration and he's a very good technical player.
"He and Nick, of the younger players, are at the top. They're very good.
"Nick has had a few injuries and has had a bit of bad luck so we feel Carrington is the best place for him at the moment [rather than sending him out on loan]. That way, we can work on bringing him on physically and preparing him for next season."