The talented 20-year-old's efforts this term have been hampered by a niggling knee problem, and the club's medical staff have advised a period of rest.
Castelen's situation will be reviewed in the next fortnight, but it is hoped that surgery can be avoided.
ADO's woes were compounded after midfielder Jan Paul Saeijs was told he needs knee surgery.
One piece of good news, though, is that striker Rik Platvoet's recent ankle operation went without hitches and he should be able to kick-start his career in around a month.
