But, despite his debut for the Hoops ending in a 4-1 thrashing - which leaves Legia Warsaw as massive favourites to progress to the play-off round of the Champions League - the Norwegian midfielder admits it could have been worse.
Which is why Berget believes it is not mission impossible at Murrayfield next Wednesday, and hopes the Polish club's failure to hammer home their advantage as much as they could have done after Efe Ambrose's red card just before the break has left the door open for a spectacular comeback in the second leg.
The 23-year-old Celt said: "It's no fun letting in two easy goals at the end, especially when Fraser Forster has saved a penalty and they have put another one wide of the post.
"It could have been five or 6-1 for them. But, at 4-1, we are still in it. A 3-0 victory in the second leg will do it for us."
Berget was a surprise starter, just two days after joining Celtic on a six-month loan and with only half a dozen games under his belt since January.
After flying back with his shell-shocked team-mates in the early hours of this morning, he has had time to reflect on a big night that did not go to plan for him or his new team-mates.
He said: "It was definitely not the debut I was hoping for.
"It became difficult for us after we went down to 10 men. We got tired at the end and gave them some easy chances and easy goals.
"But I think it's still possible for Celtic to go through. We can get the result we need.
"Of course, we will have to get the first goal - then the second goal and the third."
Celtic did manage to open the scoring in Warsaw, Callum McGregor repeating his feat from the previous qualifying round away leg in Iceland when he cut in from the right wing to hammer home a stunning left-foot shot, once again with the aid of a deflection.
The 21-year-old midfielder's strike was just what Deila and the 200 Celtic fans who had made the trip wanted to see.
But, it was all downhill from that point on for the Hoops - and now they have a mountain to climb in next week's return leg in Edinburgh.
"Of course, when we scored first we felt good but we never settled down with our play or kept the ball the way we had to do," said Berget, who, unsurprisingly, ran out of steam after an hour of playing in the 72-degree heat and was replaced by Honduran Emilio Izaguirre.
"Near the end, with us a man short, it was still 2-1, and that would have been a good result for us in the circumstances.
"We had done well to keep the scoreline to that until about 10 minutes from time.
"So it hurt to lose those two late goals and finish 4-1 down."
The little-known Berget - who was parachuted into the squad from Cardiff City after becoming boss Deila's second signing - accepts that you only get one chance to make a first impression.
But he assures Hoops fans there is much better to come - and not just from him.
"With more games I will improve and the team will too," he said.