Oster faces lengthy spell on sidelines
Oster, who is looking for a move away from The Stadium of Light, suffered a nasty looking knee injury following a challenge from behind and was immediately taken to hospital.
"It looks a bad one," reserve team boss Ricky Sbragia said. "He's gone to hospital and we think its his ligaments."
Oster is still waiting to hear the extent of the injury, but he is likely to be sidelined for some time.
To cap a miserable night for the former Grimsby and Everton wide man, he also missed an 11th-minute penalty, before being carried off shortly after half-time.