Uefa and Europe's top clubs have said allowing domestic football seasons to play out in full is of "paramount importance" and threatened those that don't with expulsion from next season's Champions League.
In a joint letter released late on Thursday, Uefa, the European Club Association (ECA), and the European Leagues body representing nearly a thousand clubs in 29 countries, said that they were working on the possibility of playing on into July and August if need be.
Europe's governing body Uefa this week suspended its own competitions - the Champions League and Europa League - at the last-16 stage to allow domestic seasons more time to finish with almost all football on lockdown to stop the spread of coronavirus that has caused thousands of deaths in places such as Italy and Spain.
"Stopping competitions should really be the last resort after acknowledging that no calendar alternative would allow to conclude the season," the letter said.
The joint response came after the Belgian Pro League announced on Thursday that it recommended declaring the season over with the present table accepted as final, with Club Brugge declared as winners. The decision still needs to be formally validated at a General Assembly on April 15.
It is the first European league to take such a measure, although more could follow, with the Premier League meeting on Friday to map out how to take their season forward.
That means Club Brugge would in theory go straight into the next Champions League group stage, but Uefa, the ECA and the European Leagues indicated that they may be barred from continental competition if the Belgian league decision is finalised.
"It is of paramount importance that even a disruptive event like this epidemic does not prevent our competitions from being decided on the field, in accordance with their rules and that all sporting titles are awarded on the basis of results," the joint letter said.
Not justified
"We are confident that football can restart in the months to come - with conditions that will be dictated by public authorities - and believe that any decision of abandoning domestic competitions is, at this stage, premature and not justified.
"Since participation in Uefa club competitions is determined by the sporting result achieved at the end of a full domestic competition, a premature termination would cast doubts about the fulfilment of such condition."
The letter concluded with Uefa saying it "reserves the right to assess the entitlement of clubs" to be admitted to its 2020/21 club competitions.
The Belgian Pro League said it had had "constructive" discussions with Uefa on Friday morning in which it "contested any approach which would force a league to continue in the current health crisis".
Uefa has set up two working groups to devise a way for European football to get out of the crisis caused by the coronavirus pandemic.
There have been calls in other countries for this season to be declared null and void, but any option which rules out completing this season could have serious consequences for leagues reliant on huge television deals and who could find themselves having to reimburse broadcasters if remaining matches are not played.
