He returned to the famous stadium yesterday but as he walked out the door this time, he did so as Celtic manager.
Few of those Deila encountered on his trip to Glasgow in November would have known who he was but now he is the most important man at the club, the 38-year-old plucked from relative obscurity and thrown into the limelight.
Of all the names in the mix to replace Neil Lennon in recent weeks, Deila's was the most surprising. Not because he wasn't qualified enough for the position, but because many on these shores were unaware of who he was or the job that he was doing over in Norway.
It will take some time for the Celtic fans to fully understand who their new boss is and what he is all about.
But the Parkhead faithful have already made quite an impression on the man who has swapped Stromsgodset for Celtic in a whirlwind week.
"I was here for the Barcelona game," Deila said. "I went to see the Celtic-Barcelona Under-19s and then to the main match.
"The day before I was at Manchester City-Bayern Munich, Under-19s and the first teams.
"That was an unbelievable experience, to be here - the atmosphere and everything.
"I almost never take pictures but I filmed that. So many times I have looked at that film, when You'll Never Walk Alone was sung before the match. I showed my girls.
"At that point I didn't know that this was going to happen.
"I've been a Liverpool fan and I think the atmosphere is much better here!"
The Champions League gave Deila his first insight into Celtic and it will soon provide him with his first real challenge.
With the SPFL Premiership crown secured before the ink was dry on his one-year rolling contract, it is in the European arena where he must excel.
He has little experience of continental competition but with three rounds of qualifying to negotiate to secure Celtic's seat at the top table, he must learn quickly ahead of the games that will make-or-break his first campaign.
"You can draw very good teams and you can be unfortunate because it's a cup and that's hard," Deila said.
"But we need to have a good pre-season and take it from there. We know the quality and the hunger in the squad to get to the Champions League.
"When you get something, you want it even more next time.
"If we go out, then we go out and we have to work harder.
"But I have a good feeling that we are going to succeed."
Results will determine Deila's fate as Celtic boss in the coming months and years but the means is just as important as the end for the 38-year-old.
He has travelled across Europe to study different coaching methods and received a message of good luck from Borussia Dortmund's Jurgen Klopp in the hours after his unveiling yesterday.
The German said: "A great club with great fans gets a great manager. I'm very happy for Ronny Deila and wish him every success at Celtic."
Deila brings a fresh approach and a fresh vision to Parkhead but his eyes remain fixed on the silverware.
"I think a lot of this business is about results, it is very important, we need to win games and trophies," he said.
"But I have to go behind that and think, 'what can I do to get the best out of the team' and really work with the culture.
"If we talk about developing, people say 'oh developing, we don't care if we don't win' and that is true.
"For me, that is what you do to win. You work with the boys and the staff and get the most from them."
At a club where it is all about the winning, Deila's passion for success should stand him in good stead.
He famously stripped off after guiding his Stromsgodset side to Tippeligaen safety and is determined to experience more euphoric highs.
He said: "I'm an emotional guy. I love to win, of course. But the best thing I know is when you have a good performance on the pitch and you win and the atmosphere is like what is was like here for Celtic vs Barcelona.
"When I'm driving the car home at night, I get goosebumps when I think about it.
"That is football. It's fun to win, but the way to win is the most fun thing. I hope I can sit in my car driving to my apartment somewhere and feel that emotion."
With the formalities now completed, Deila can get down to business at Celtic.
It is likely that former Hoops midfielder John Collins will be his first appointment as assistant manager while Craig Gordon is also in talks over a move to Parkhead this summer.
He is the third foreigner to have his name on the manager's door but is unlikely to return to his former club for help.
"I don't think so," he said. "It is really important to have people who are from Scotland and from Celtic. You never know what will happen, maybe foreign people or players will come.
"For now, I have to get control of everything and then we will see what is best. There are a lot of good people working in Scotland."