Di Canio has already signed nine new players this summer, but he feels there is a key piece of the jigsaw still missing.
"The club is working on the two full-backs, but more important to me is the need to get a key player in central midfield, someone who's English," Di Canio told the Sunderland Echo.
"He needs to be English, with a physical presence, because we have analysed that is a need we have.
"English, because he needs to know English football inside out, and also a player with very good quality because we want to play attractive football which gets good results."
The Black Cats have been linked throughout the summer with Spurs' Tom Huddlestone, although nothing has yet been agreed.
Di Canio, meanwhile, has no concerns over the fitness of centre-back Wes Brown and striker Ji Dong-won after both missed Wednesday night's 1-0 pre-season win at FC Midtjylland through injury.
"Wes had a little problem and we decided not to risk him on the day," added Di Canio.
"As for Ji, he has been out for a few days, but we expect him to be back in training in the next few days.
"So at this moment in time we do not have any real worries about either of them."