The Scottish Premiership matches of champions Celtic and Aberdeen will be postponed due to breaches of Scotland's strict coronavirus quarantine rules in a "yellow card" to the sport, First Minister Nicola Sturgeon said on Tuesday.
Sturgeon warned that clubs would put the new season in jeopardy if they failed to respect the rules.
Celtic's game with St Mirren on Wednesday will not go ahead after Belgian defender Boli Bolingoli admitted he had failed to observe quarantine protocols after a trip to Spain. Anyone returning to Scotland from Spain must spend two weeks in quarantine.
Bolingoli, 25, played in the 1-1 draw with Kilmarnock on Sunday, the team's second match of the season.
The Scottish government is already furious at eight Aberdeen players who visited a bar last week. Two of them subsequently tested positive, forcing the postponement of last Saturday's game with St Johnstone.
Aberdeen's home game with Hamilton on Wednesday is now off as well and Saturday's match between Celtic and Aberdeen has also been postponed.
- 'Yellow card' -
Sturgeon said Bolingoli's case was a "flagrant breach of the rules."
"As a minimum, you should not be expecting to see Aberdeen and Celtic play over the course of the coming week and we'll see what the other conclusions are," said Sturgeon.
Sturgeon -- whose administration by coincidence held talks with Premiership managers and captains on Monday -- issued a thinly-veiled threat.
"Consider today the yellow card. Next time it will be the red card because you will leave us with absolutely no choice."
Although Bolingoli apologised for his behaviour, Celtic did not hide their fury in a statement released later on Tuesday, saying: "It is difficult to imagine a more irresponsible action in current circumstances."
Bolingoli apologised to his manager, teammates, supporters "and so many others for letting them down so badly".
"I am guilty of a major error of judgement," the 25-year-old added.
"I know what I did was wrong and I know that I must now deal with the consequences."
Celtic said Bolingoli would feel the full force of their disciplinary procedures.
"Celtic 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," the club said.
"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."
Celtic manager Neil Lennon said he was "absolutely livid" at what he called "a total betrayal of trust."
Steven Gerrard, manager of Celtic's bitter rivals Rangers, said the message coming out of the talks with the administration had been crystal clear about clubs' responsibilities.
He said the "severity" of the warnings had shown "how important it is that everyone behaves in the right way".
"And it is a concern and a worry because if mistakes continue to happen, there is no doubt about it, the football season will be cancelled and that's not what I want or what anyone wants at Rangers, or throughout Scottish football."