The 32-year-old struggled through the closing stages of last weekend's 0-0 draw with Aston Villa but is winning his fitness race ahead of the Blues' visit to the Stadium of Light.
Black Cats manager Gus Poyet told the club's website: "Surprisingly it was not what I thought it was, a muscle injury.
"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."