Old Firm hat-trick hero Dembele, 20, was the spot-kick villain on the Hoops’ heaviest-ever Euro defeat to brilliant Barcelona.
Lionel Messi bagged a hat-trick and Luis Suarez scored twice as Celts shed seven just three days after putting five past Rangers.
And boss Rodgers insisted post-derby tiredness as well as Dembele’s missed chance to level at 1-1 were the key reasons for the Champions League calamity.
He said: “We put huge effort into the weekend and we got a fantastic victory. It was always going to be really tough in the next game to play the best possession team in the world.
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“We had a massive moment in the first half. We went 1-0 down very early but we had a great chance to level the game.
“If you get a penalty and get the score to 1-1, it makes it a little nervy — especially after them losing here at the weekend.
“But after that, they scored a second goal and, in the second half, we ran out of legs. The game at the weekend, added to their immense quality, made it hard — and the scoreline is bitterly disappointing.
“It was always going to be tough but you have to try to give them something to think about. You don’t get many opportunities at a place like this, so you have to put the penalty away.
“Moussa has been brilliant since he came here but Marc-André ter Stegen read his penalty, saved it and then they went 2-0 up and it was very difficult.”
Barca boss Luis Enrique’s superstars didn’t let Celts off the hook — and Rodgers admitted it was a steep learning curve for the Hoops.
He added: “This is a competition which is going to be a brilliant learning season for us. Tonight is one of those nights you have to take.
“There can be no embarrassment because they have done it to better teams than ourselves. It’s tough to take when you lose so many goals.
“They didn’t work any harder than our players, but the confidence, technique and ability to accept the ball under pressure are things you can learn.
“They are very special players. I had the great fortune to work with one of them and Luis was at his top level.
“We had five in the back line but their movement, speed and touch can make it very difficult for you. They are world-class players and showed it.
“You can’t be too downhearted. Whether you are playing Barcelona or Berwick Rangers, there is professional pride to play for. No team likes to lose like that.
“But this won’t hamper us in any way.”