Diakite is off contract in June.
"It was almost all done with Napoli. Unfortunately, we have different time-sensitive requirements and have therefore decided to take different paths," agent Ulisse Savini told lalaziosiamonoi.
"English football is intriguing and Di Canio has brought great enthusiasm, but for now I haven't spoken to anyone from Sunderland. If they were to call, we'd be honoured to talk to them."