Yes it is *harder* to sell them because it is only levels above that see him, and of course an MC is harder still because there are always many to choose from, and if he has bad ratings, he won't look like much of an upgrade to the managers that see him for sale.

At worst you might have to wait till next season day one to sell him. I would train the living heck out of him and add to his physical a bit and see if his play improves. And continue training him so he has chance to improve and improves chances of selling him!