The Hoops went into the game having already qualified for the last-32 and were without several first-choice players for various reasons but another night of indecision at the back means they have lost 19 goals in 12 European ties this season.
The Scottish champions fell behind to Marko Pjaca's strike after 14 minutes before goals from Kris Commons and Stefan Scepovic had the visitors ahead.
However, Pjaca levelled with a deflected shot and he claimed his hat-trick five minutes into the second half after the lead had been regained through Marcelo Brozovic, as Celtic rocked.
Dinamo defender Josip Pivaric put through his own goal with nine minutes remaining and - although Scepovic almost grabbed a late equaliser with a header - the Parkhead side were left with eight points from six games and knowing they need to improve against whoever they are paired with when the draw is made next week.
Deila said: "It was a poor performance
We were not 100 per cent and there was a lack of intensity and aggression.
"It was disappointing that we weren't up for the game.
"We scored three goals, that was a positive and I think the substitutes (Darnell Fisher, Liam Henderson and Anthony Stokes) were positive when they came on, but defensively we gave away too many chances and conceded four goals.
"You should win when you score three goals away in Europe.
"Individually, there were some bad performances but also as a team, as a back four we dropped too much as a back four and there were a lot of space between the defence and midfield and they got three chances from that at the start of the second-half.
"We were talking before the game about being compact and no balls in between us and we didn't get that at the beginning of the second half."
Ahead of the match, Deila said he was mindful of the struggle to beat Dinamo 1-0 at Parkhead in October and admitted Celtic would have to improve regardless of whom they face when the competition resumes in February as they go into the pot for Monday afternoon's last-32 draw.
Deila added: "We were too open, that was the problem.
"We had the chance to win at 2-1 and it was disappointing that we gave away the victory.
"We have to take this with us to the next stage.
"We have the players but we have to think about the formation when we play away in Europe and what kind of players we use.
"We were more offensive than we have been and we conceded too many goals."
The Norwegian admits he will have a re-think on tactics for the knockout stages, and he added: "We have to be a lot, lot better in the next round.
"We will have players back who will give us more spirit so I am not frightened about that
But it was disappointing to give the victory away like we did, from being 2-1 up."
Dinamo coach Zoran Mamic was pleased with his side's victory but hoped they had showed that former earlier.
Dinamo, who ended up finishing third in the Group D table, had no chance of qualifying for the knockout stages ahead of Thursday's match as they had collected just three points from their five matches - despite getting off to a winning start in September with a comfortable 5-1 victory over Astra
He said: "We were more dangerous than Celtic, we made mistakes for two of their goals.
"I am sorry we didn't play at this level from the beginning."
Source : PA
Source: PA