Kilmarnock's Scottish Premiership match with Motherwell has been called off with the home side's entire squad advised to self-isolate for 14 days.
The game at Rugby Park was due to take place later on Friday but all home players have been told to stay away.
It follows Kilmarnock confirming a further three Covid-19 cases late on Thursday after three positive tests earlier in the week.
The SPFL board agreed with the Ayrshire club's request to postpone the game.
However, the league will now investigate "the circumstances leading to the postponement" and will not set a new date until that has been concluded.
Kilmarnock said all six players were either asymptomatic or are experiencing mild symptoms and that a deep clean of the stadium would take place.
Motherwell say the "right course of action has been taken" and "wish those affected a speedy recovery".
The SPFL board will reconvene on Monday to discuss Kilmarnock's next two fixtures - away to Falkirk and at home to Dunfermline in the Scottish League Cup - which fall within the self-isolation period.
Competition protocols published last month suggest that if they are unable or unwilling to field a team in those games, they would forfeit the match 3-0.
How did it unfold?
Manager Alex Dyer said one player felt unwell on Sunday after the victory at St Mirren the previous day and was not allowed to train.
Following a round of Covid screenings the following day, he and two others returned positive tests, although the latter pair were asymptomatic.
Late on Thursday, Kilmarnock announced three further players had the illness after a fresh batch of tests and would undergo further NHS screening.
Then, early on Friday, it emerged that the entire squad had been advised to self-isolate for 14 days following contact tracing.
A statement from the Scottish FA and SPFL joint response group said: "This is in order to minimise the risk of further cases in the staff group and wider local community and to support Test and Protect."
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