It might take another six weeks for the real cost of that concession to become clear.
On Tuesday, Lasse Schone's goal meant little in terms of the result.
However, Celtic could still regret not keeping a clean sheet if they lose to the Dutch champions in Amsterdam and go on to finish level with Frank de Boer's side on points in Champions League Group H.
Then the head-to-head between the clubs would come into play, and Schone's shot might have a golden legacy.
Of course, the best way for Neil Lennon's side to avoid such a sickening scenario is to deny Ajax victory by any margin on November 6.
And Virgil van Dijk is already planning to help that happen.
Since Tuesday's game, the 22-year-old defender has been swamped with calls from friends back in Holland echoing the view of de Boer and midfielder Daley Blind that the Hoops rode their luck at Parkhead to deny the Dutch a merited victory.
Van Dijk couldn't care less. And he admits he will be just as content if his countrymen are repeating the gripe after the game in Amsterdam.
He said: "I would be very happy if they are.
"I hope we get the three points in Amsterdam as well."
Clearly, van Dijk is not about to embark on any career in diplomacy. He has been around the block - or the canals - long enough to know the only stat that matters is the one which displays the final score.
So, unlike their famous Edam or Gouda, it is simply hard cheese for the Dutch.
"Everybody thought the same about it, that Ajax was the better side and we won with a lot of luck," he reported on the reaction in his homeland.
"But, we deserved the win with our power and passion.
"The fans keep on surprising me. When we were in the huddle, you could feel them.
"So, the reaction from Holland doesn't annoy us. We were just happy to get the three points and stay in the group."
Van Dijk has no intention of using the fall out from this week's game as an extra spur for the return.
"We don't need any extra motivation," he explained.
"We know what we are capable of, and we can get at least a point in Amsterdam.
"If we get a result there, of course, we have a good chance of getting to the next round.
"But Sunday is the next game for us, and we have to focus on that.
"We want to get the three points and stay unbeaten in the league."
That is the level-headed approach which has so impressed Lennon since Van Dijk arrived in Glasgow from Groningen. Unfortunately, for the Hoops boss, he is not the only one who reckons he can be a star.
But Lennon is not about to cash in quickly on the flying Dutchman. Asked if he believes there may be interest shown in him when the window re-opens mid-season, Lennon replied: "Probably - but he's not for sale in January. Virgil has just come in the door, so let him progress.
"If he keeps going the way he is at the minute, then it's inevitable there will be suitors for him - as with a number of other players here."
Champions League football may be turning the spotlight on Van Dijk and Co. but it is also building a security wall around the club's assets.
Lennon said: "There's an onus to sell sometimes if you don't have Champions League football.
"But now we are stable and don't need to sell anyone."