Former Sunderland chairman Niall Quinn remains puzzled by Martin O'Neill's dismissal last season.
O'Neill is now preparing for his debut as Republic of Ireland coach.
"When I left I did feel Martin O'Neill was the right man and it would go from strength to strength," said Quinn.
"I am as puzzled as any Sunderland fan as to why that relationship - Martin O'Neill and Sunderland Football Club - isn't still going and isn't thriving.
"The Paolo Di Canio thing, we now know, was a debacle in many respects. Everyone will remember the Newcastle result (a 3-0 win). But it was not to be."
