I already answered similar questions multiple times, but happy to answer it again. I think physically and techincally he's ready for the Championship. What he, however, needs time with is the pace of the league and I hope Sunderland fans are patient with him because of this. Players who are much more experienced and who come from better leagues than Serbian league, e.g. the Italian league or the Dutch league often struggle at first with the pace of English football. Serbian league is much slower than PL and significantly slower than Championship as well. Once he adapts to the pace of the league, I'm sure he'll be a success. But it's hard to tell whether it will take him 5-10 minutes or 5-10 months. I hope he'll adapt very quickly and be a real asset for you this season and hopefully you can get promoted.
Sounds promising, let's hope he has the right attitude as we have many skilful players, both young and old but with the wrong attitude.