The Doc remains hopeful that United can turn things around - starting with a good transfer window this summer.
He told the Manchester Evening News: "When Fergie decided to call it a day and David came in, he was an excellent choice. I still think he's an excellent manager but we all make mistakes.
"There's an old adage in football, 'if it isn't broke, don't fix it'. Changing the backroom staff maybe was David's mistake. The coach under Fergie, Rene Meulensteen, was fantastic. He was so successful with Fergie, it was quite a surprise when he left.
"No matter who was the manager, it was always going to be difficult for the person succeeding Fergie - we always knew they would need time to settle but perhaps keeping the backroom staff would have provided some stability and helped David and the team. Hindsight is a wonderful thing."