Denying someone their profession when it has nothing to do with the offence is hardly likely to facilitate rehabilitation, which is part of our justice system. If some one loses their means of earning money they either become a burden on the state or turn to other ways of making money. In this particular case, he probably has enough money to survive, but the general principle still applies.
Placing him on the sex offenders register is to protect the vulnerable, not to further punish him. This will inevitably affect employment in some areas, where there is contact with young or vulnerable people, e.g. as a teacher, but being a footballer is an isolated job. Where there could be a risk it is easily mitigated, by restricting contact with youth teams, excluding from school visits and mentorship programmes.
Ultimately the question has to be is he more likely to reoffend if he is allowed to continue his career, giving him something to focus on, or if he is denied the profession chose, probably the only one he has qualifications for, and left without what his main motivation in life and with time to fill. The question is not how do we continue to punish this brick because we don't like him and what he did. He has completed his punishment in the eyes of the law and the sex offenders list is to protect the vulnerable, not to continue punishment.