The 25-year old goalkeeper has joined Liverpool on a Â£9million deal and although Di Canio will now have to find an apt replacement, he does not begrudge the former Sint-Truiden man.
"Simon is a fantastic footballer, a fantastic professional and a fantastic lad and I would like to personally thank him for his contribution to the team last season," Di Canio told the Black Cats' official website.
"He was crucial to what we achieved and he goes with the very best wishes of everyone at the club.
"I would like to assure our fans that there is a huge amount of work going on behind the scenes. Our aim is to build a competitive squad for the new season and this deal will give us further ability to strengthen the side."