Celtic defender Boli Bolingoli travelled on holiday to Spain without telling the club, prior to the weekend’s match against Kilmarnock, The Scottish Sun reports.
The paper say that the left-back has angered club bosses after failing to declare the trip or self-isolate following his return from the pandemic hit nation.
He would then go on to play in the fixture, coming off the bench late in the game.
Bolingoli has since been tested for coronavirus, with the results negative, but there appears to have been a serious breach of protocol.
The report states that Celtic are furious with the player.
The defender told The Scottish Sun: “I have made a huge mistake. I want to apologise to my manager, my teammates, the supporters, everyone at Celtic and so many others for letting them down so badly.
“I am guilty of a major error of judgement. I know what I did was wrong and I know that I must now deal with the consequences.”

Meanwhile, a spokesperson for the club told the paper after launching an internal investigation: “Celtic Football Club has taken its response to Covid-19 extremely seriously and we are pleased that, to date, we have recorded no positive tests.
“Our staff have given so much in this area, working tirelessly to ensure that all players and other club personnel are safe, fully aware of their own responsibilities and familiar with all guidance and protocols.
“Safety must always be our priority. Clearly, a full investigation will now take place and the Club will take all appropriate action.
“Subsequent to the player’s return he has recorded two negative tests in the past week.”
This is clearly a disappointing development and it’ll be interesting to hear what Neil Lennon has to say later in the week when he is no doubt asked about the issue.

Bolingoli has already struggled to make progress in the first-team, with Greg Taylor now installed as a first-choice pick in his position.
With the defender already heading towards the fringes of the squad, could these actions now push him towards the transfer exit door?
That’s the question on my mind this evening.
The report comes after Aberdeen stars drew the ire of Scottish football and First Minister Nicola Sturgeon last week when they were found to have socialised in city-centre bars and restaurants, which prompted a large videoconference meeting with the SFA today.
In other news, Celtic are said to be close to agreeing personal terms with striker Albian Ajeti.
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