The defender picked up a knock during the Black Cats' goalless draw at Aston Villa on Saturday.
However, Poyet is confident that O'Shea will be able to play against Chelsea at the Stadium of Light.
"Surprisingly it was not what I thought it was, a muscle injury," he told the club's official website.
"It was a movement that he had not had before - he was sure that it was not a massive injury but he didn't know what it was, so we needed to wait 24 hours.
"He has trained today and everything was fine, touch wood. Let's hope John will be there tomorrow."
Sunderland are currently five points from safety in the Premier League table.