Celtic's controversial trip to Dubai was "clearly... a mistake" and one for which they "profoundly apologise", says chief executive Peter Lawwell.
Neil Lennon and his squad returned from training in the Middle East on Friday, with Christopher Jullien subsequently testing positive for Covid-19.
As a result, Lennon, assistant John Kennedy, and 13 players had to isolate and missed the draw with Hibernian.
"The outcome was clearly very regrettable," Lawwell told CelticTV.
"On reflection, looking back and looking with hindsight and looking at the outcome of the trip, clearly it was a mistake and for that I profoundly apologise to our supporters.
"This horrific pandemic has affected the whole of society. It's affected people here in Scotland, it's affected our supporters, it's affected our football and it's affected our club - probably our club more than any."
Jullien is the fifth Celtic player to test positive for Covid-19, with David Turnbull, Odsonne Edouard, Nir Bitton and Hatem Abd Elhamed previously contracting the virus while on international duty.
On Saturday, Celtic assistant manager John Kennedy admitted the club had been guilty of "minor slip-ups" in Covid-19 protocols during their six days in Dubai.
Photos emerged of members of the Celtic party not distancing or wearing face coverings, and Kennedy said they give a "bleak" but "false" impression.
Speaking on Monday, Scotland's First Minister Nicola Sturgeon urged Celtic to "reflect seriously" on events that have led to the recent outbreak.
But Lawwell said the decision to go Dubai, where Celtic have trained during the winter over the past four years, was made with "the best intentions".
And he cited Celtic's earlier international trips this season, after which there had been no positive tests.
"Clearly the landscape has changed significantly - particularly in the run-up to us going to Dubai - in terms of the infection rate," he said.
"The protocols were robust, they're proven, and that's what we put in place for the Dubai trip.
"Overall, the decision to go was for the right reasons - it was performance - and of course the outcome of that has been really disappointing."
Celtic are now 21 points behind Scottish Premiership leaders Rangers but with three games in hand and the chief executive described some of the criticism of the club as "unfair".
"I do understand how people are questioning the decision to go," he added.
"We've got to keep fighting over the coming months and put the club in a position that we can maximise the potential and take this magnificent football club as far as we possibly can."