Riseth believes the loss to Rangers was the final straw.
Riseth had plenty to say, believing Deila did his best with the tools he was given, but despite this he labels the current team one of the worst Celtic sides of all time.
He said: "What I have seen of the team is not good. I've seen some games .. This is one of the weakest Celtic teams of all time.
"I would say that he did an good job. He leaves from there with titles. For Ron's resume is fair enough, but he did not succeeded in Europe. The cup exit against Rangers was too bad for the team. Celtic is a demanding club."
To Deila's credit he is on course to win a second league title out of two, but the failure to qualify for the Champions League in successive seasons was a critical loss, which made the long procession to the league title seem less valuable.
Deila issued a statement on Celtic's official website on Wednesday explaining he would be stepping down as manager at the end of the season. No replacement has yet been appointed in his place.
Riseth, 43, played for Celtic briefly between 1998 and 2000, winning the Scottish League Cup.