Hi Trainers

I was wondering what happens to a player who is training a new position (or special skill) if you sell him. Lets say a 99% player training new position with progress of 14/50. What happens to that progress when i sell him? I have some young players on 99% and i want to avoid getting them the 6th star. Because i am getting offers including tokens. Simply not training them is easy but what to do with those training point gifts. If it randomly hits my 99% player? Thats why i was thinking of letting them learn a new position so the 99% won't get affected. Is this idea good for preventing the 6th star?

Best regards