Deila rested 10 players from the team which earned a 1-1 draw with Maribor in Wednesday’s first-leg Champions League qualifier in Slovenia.
The visitors squandered several good chances in the first-half at the Tulloch Caledonian Stadium but found Inverness keeper Dean Brill in fine form before a cruel deflection off young Celtic defender Eoghan O'Connell settled the match on 65 minutes.
But with Tuesday's return against Maribor at Celtic Park looming, Deila reckoned he had to take a gamble against Caley Thistle.
"I learned a lot about the players that came in but maybe there were too many new players," Deila said.
"There were probably too many at the same time and we didn't get the performance we wanted. We now have to focus on Tuesday.
"I have to congratulate Inverness because they played well but we had the better chances in the first half.
"You will see on Tuesday if I regret making too many changes, but of course it will be worth it if we win."
Inverness counterpart John Hughes was delighted his team cemented their place at the top of the Scottish Premiership with their first home win over Celtic in over three years.
"To beat Celtic and to keep a clean sheet is absolutely different class," Hughes said.
"We rode our luck a bit in the first half and had Dean Brill to thank for a few saves. But to beat them you need that luck.
"I totally understand them making that many changes and, to be honest, I would have done the same in their position. They have a massive game on Tuesday.
"I wish them well. I do, because it's good for Scottish football.
"But we played some real good stuff, created a lot of chances and showed a desire to keep a clean sheet."