Former Everton midfielder Oster has sat out the last three matches with a hamstring injury and is not expected to recover in time.
Ex-Celtic and Swansea striker Beattie was also forced to miss last weekend's 2-1 defeat at Plymouth with a hamstring problem and he will be checked over.
Player-manager Edgar Davids has drafted in Watford midfielder Ross Jenkins on a month's loan so he could make his debut.
Davids is still without forwards Ricky Holmes (foot) and Steve Kabba (knee) but Luke Gambin pushed his claims for a start with a goal for the reserves in midweek and fellow striker Jamal Lowe is back from a loan spell at Boreham Wood.
- Sports & Recreation
- Edgar Davids