The Court of Arbitration for Sport (CAS) rejected Legia's final appeal to be reinstated into the Champions League qualifying play-offs on Monday.
The Polish club fielded an ineligible player in the second leg of their third-round qualifying tie against Celtic, which saw them forfeit the match and essentially allow the Scottish champions to progress in Legia's place.
Legia had an initial appeal rejected by UEFA before CAS sided with Europe's football governing body, and with the first leg of Celtic's play-off against Maribor set for Wednesday, Berg and his players know they have to give up on their dream of playing in the Champions League group stage.
"This is as expected. When UEFA refused a quick handling of the case as it stood, we saw that it was most likely that we would not be successful," Berg told Norwegian newspaper Dagbladet.
Legia defeated Celtic 6-1 over two legs in the third qualifying round.
But, after Berg's side forfeited the second leg, following the introduction of ineligible substitute Bartosz Bereszynski in Scotland, Celtic were awarded an automatic 3-0 home win, which saw them progress on the away goals rule after the first leg finished 4-1 in favour of Legia.
Bereszynski had received a three-match suspension in Legia's final UEFA Europa League game last season and although he did not play in his club's first three Champions League qualifyiers, he was not registered for the first two, prompting UEFA to rule he had only served one match of his ban when he took the field against Celtic on August 6.
Berg still cannot believe his team are being punished for a clerical error.
"It sucks. We defeated Celtic 6-1," the Norwegian coach said.
"The player in question was missed the first three Champions League matches. The error was that his name was not on the list of 25 [registered] players in two games.
"If [his name] had been there, we would have been in the play-off. It sucks, also considering that it is 18 years since a Polish team was in the Champions League [group stage].
"The guys had worked well towards this but we miss out on an administrative error."
CAS claimed on Monday they will continue to look into the matter with Legia asking for compensation from UEFA but Berg conceded it would be scant consolation.
"We hope to gain favour but we will not go into the Champions League again. The adventure is over," he said.
Legia must now turn their attention to the UEFA Europa League with a two-legged play-off against Kazakhstan's Aktobe set to start on Thursday.
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