"I had my bad injury and going to Grimsby was always going to be about me getting some match practice," Oster told the Grimsby Telegraph.
"I've only played in a couple of games as a substitute since I've been back at Sunderland. But the team isn't doing too well and you'd think you'd get a chance. Hopefully mine will come in the next couple of games.
"I want to get back in the side and play. That's what I'm concentrating on now. Getting back playing first team football with Sunderland."