The Hoops defender was sent off for a challenge on Accies striker Carlton Morris just outside the box during the 1-1 draw.
Afterwards, Deila said the decision was correct but at the pre-match press conference ahead of the Ladbrokes Premiership game on Wednesday night, he had changed his mind.
He said: “I have seen it many times and when I have seen it from all angles, I think it is a wrong decision because he was on the ball.
“We will therefore appeal it.
“Okay we got punished to go down to 10 men but hopefully we won’t get a suspension.”
Deila admitted it was a “tough decision” for referee Craig Thomson and reiterated his belief that his defenders should not readily go to ground .
The Norwegian said: “I am still saying that I want my defender to stay on their feet because we have quick defenders and to run with people is better than taking chances and putting the ref in a bad situation.
“It is not about Dedryck, it is about everybody in the defence. We have had some issues with red cards before and when you play a high line and press a lot, there is a lot of space behind us sometimes and we get into this situation where it is one versus one and it is something we talk about all the time.
“We want players to stay on their feet so we want them to run with (opponents) and not make bad decisions.
“That is the perspective from a coaching point of view but when he gets the ball, then in my opinion it is not a red card.”
The former Stromsgodset boss was criticised for not defending Boyata, most publicly by former Celtic striker Chris Sutton, but he denied those accusations.
He said: “One thing for me, it is important to be honest.
“I will never say anything negative of a player personally, but this is a decision on the pitch and that is something everyone has seen and I don’t see any problems with that.
“I am honest with the players, and I spoke with Dedryck and that is no problem.
“This is not an attack on him. I have defended and I will defend the players.”
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