I really don't think he is using any (at least conventional) concealers,think about it,being a professional footballer,apart from major sweating his head will constantly get touched by the football,and even other players body,that will definitely wipe some of consealers off.there is no doubt about it. and add to that professional hd cameras zooming on his face..
do you really think he will put himself in such awkward situation even if there is minimal risk?why would he do that? he could just have that thin look in the field and blame it on sweating,etc and look dense in magazines,interviews etc until his hairs fully grow.after all he was looking so bald all these years,surely he could cope with it for another year?
how his transplant hairs look so great so soon remains a mystery.