Now the Hoops will proceed to play NK Maribor in the Champions League play-off, with the first leg in Slovenia on Wednesday.
More than 24 hours of tension was finally brought to an end when the Appeals Committee's decision was made public.
Legia had been confident their presentation at the hearing in Nyon, Switzerland, yesterday morning, had been successful.
They had argued the decision by the the Control, Ethics and Disciplinary Body to forfeit the match they won 2-0 against Celtic at Murrayfield last week was flawed.
They accepted they had fielded Bartosz Bereszynski as a substitute when he was still serving a suspension.
But Legia insisted it was an administrative error and contested the punishment, an automatic 3-0 victory to Celtic, which saw them go through on away goals as the aggregate score was then 4-4.
The Polish club also highlighted what they believed were procedural irregularities as the original case was decided by just one member of the Control, Ethics and Disciplinary Body ahead of the play-off draw last Friday.
They also believed they should have been able to present their defence in person at the meeting.
However, Uefa have decided the process was not flawed, and that the decision to forfeit the match, as per their rules for fielding a suspended player, was correct.
So, Celtic can now push ahead with their plans to travel to Slovenia next week for the first leg of the play-off which they hope will get them into the group stage of the Champions League.
Legia will drop to the Europa League, where they play Kazakhstan side, Aktobe, in the play-off for the group stage of that competition.
But they have not given up the fight for re-instatement and will take their case to the independent Court of Arbitration for Sport.
It is considered unlikely any case would be heard ahead of Celtic playing Maribor on Wednesday, or that CAS would attempt to have the tie delayed to give them time to call and decide upon the case.
The Bhoys released a statement on their official website, which read: “We have been advised by Uefa of the decision of the Uefa Appeals Body to dismiss an appeal by Legia Warsaw. We understand that Legia Warsaw may appeal that decision to the Court of Arbitration for Sport.
“For our part, we can only proceed on the basis of Uefa’s decisions and the fixtures announced by them and, therefore, we must now prepare for our match against NK Maribor next week.”
Celtic boss Ronny Deila is relieved Uefa have not bowed to the pressure Legia have tried to place on them since the rule infringement was spotted by one of their Swiss delegates a week ago today.
Deila revealed he has had Maribor watched, and is aware that they sent a representative to run the rule over the Hoops as they defeated St Johnstone 3-0 at McDiarmid Park in their opening SPFL game last night.
He said: “Maribor are a good team, but Legia were a good team as well.
“Nothing is easy, But we can do much better than we did against Legia.
“And we play the home game at Celtic Park, so those two things can be good for us.
“But first we have to concentrate on Saturday when we play Dundee United.”
Deila is relieved to be going into that game when the league flag will be unfurled with three points on the board, and a first Premiership win under his belt.
And, just four days before they return to European action, Deila does not want the occasion to fall flat. He said: “We’re going to go into that game with hunger and the right attitude. We’ll do everything we can to deliver a good performance.”
Deila will have Charlie Mulgrew back from suspension for that game, and Leigh Griffiths, if the striker has recovered from the illness which the manager revealed kept him out last night.
But the prospect of James Forrest getting further game time ahead of the Maribor ties is even more heartening for the Norwegian.
Deila said: “Every team wants a James Forrest. He’s very important to our team. But he needs matches, and that’s why he only played 58 minutes against St Johnstone. We have to take care of him to make sure he doesn’t get injured.”
Deila elected to go with Craig Gordon at Perth.
But even though Lukasz Zaluska saw his long-waited chance to become No.1 following the sale of Fraser Forster slip from his grasp, the manager has encouraged the Polish keeper not to let his head drop.
“It is hard, and Lukasz will feel sorry he was not selected because he is a good player,” said the manager.
“But I’ve seen good things in Craig, and he played well in this game.”