The 19-year old attacking midfielder has been training with United for most of 2010 after joining as a guest player in March and he will be available for selection pending receipt of his International Transfer Certificate.
United general manager Dave Kasper was delighted to welcome the younger brother of former DC midfielder Fred to the club.
“Junior is a young player who has shown to us that he has the potential to become a good professional,” said Kasper. “He has very good attacking qualities and can play a number of positions in midfielder. We look forward to getting him integrated into our team.”