The rumour mill is linking Hoffenheim keeper Koen Casteels with Charlton. The 6ft. 5 ins. keeper is a member of the Belgian World Cup squad, having appeared nine times for Belgium's under 21s. He broke his shin towards the end of the season, but has evidently recovered.
I would emphasise that this is a rumour for which there is no independent verification, but it is an interesting possibility.