Celtic have condemned Boli Bolingoli following his breach of quarantine rules, calling him "irresponsible" and referring to his "stupidity".
As reported in the Scottish Sun, Bolingoli flew to Spain without informing the club, failed to isolate after returning and played in his side's Premiership match against Kilmarnock on Sunday.
News of his actions, coming just days after eight Aberdeen players apologised for going out drinking after their game against Rangers, has led to the Scottish Government considering whether to pause Scottish football.
In a statement released on the club's official website, Celtic said: "Celtic Football Club unreservedly condemns and apologises for the behaviour of the player Boli Bolingoli in travelling to Spain without informing the club and in failing to observe quarantine restrictions.
"It is difficult to imagine a more irresponsible action in current circumstances and we find it beyond explanation. The Club will take immediate action through our own disciplinary procedures.
"Celtic are in touch with every SPFL club today, and with all relevant authorities, to apologise for the fact that one of our employees has created so much additional difficulty through his actions.
"All of our playing and backroom staff have been tested twice for Covid-19 since this incident and all, including the player in question, have tested negative. While this comes as a relief to all concerned, it in no way diminishes the seriousness or stupidity of the player’s actions.
"Since the Covid -19 crisis began, we have had a safe and healthy squad of players, recording not one positive test. As a club, we have worked tirelessly to ensure a sustained, safe environment for all.
"We have led the way in working with the football authorities and Scottish Government to establish the most rigorous, effective protocols and working practices, which ultimately led to the resumption of football. We could have done no more in this area.
"It is a matter of the deepest regret to us that the behaviour of one individual has jeopardised that reputation and reflected discredit on football more generally."
Bolingoli played the final three minutes as Neil Lennon's side drew 1-1 with Kilmarnock in the Premiership.
