UEFA says its member national associations must follow "objective, transparent and non-discriminatory" principles to decide which clubs should compete in the 2020-21 Champions League and Europa League if they cannot finish their seasons.
It stressed that competitions proposing to terminate early must provide "legitimate" grounds to do so.
As a result, play-offs could decide Champions League and Europa League qualification in countries across Europe should the impact of the coronavirus pandemic force domestic leagues to be cut short.
UEFA defines those legitimate grounds as an official order from government or other authority prohibiting sporting events, or an inability to play on due to insurmountable economic problems and where to do so would put at risk the long-term financial stability of the competition concerned.
UEFA still recommends its national members aim to complete the 2019-20 season if at all possible.
A fixtures working group is looking at two scenarios - in the first the European club competitions would run in parallel with domestic action, as they do in normal circumstances, or in the second domestic matches would be completed before continental competition restarts in August.
In the event that a competition cannot be completed in full, the first preference of UEFA's executive committee after that would be for a restart "with a different format in a manner which would still facilitate clubs to qualify on sporting merit".
This suggests it would be keen to see play-off matches taking place among teams in the mix for European places if that is practical, but playing the full remainder of the season is not.
UEFA will reserve the right to refuse or evaluate the admission of any club if the grounds for prematurely concluding the season are not deemed legitimate, or the process for selecting clubs is not deemed to be objective, transparent and non-discriminatory.
It will also look at a team's admission if there is "a public perception of unfairness" in their qualification.
The association's medical sub-group is working alongside the European Leagues umbrella group and the European Club Association to link the work already done by national leagues on protocols for a safe return to training and match action.
Meanwhile, UEFA also confirmed that Euro 2020 would still be the official name of the tournament which has now been moved to the summer of 2021, to avoid the destruction of branded material already produced.
Options for the rearrangement of the European Under-21 Championship, due to be played in the summer of 2021 in Hungary and Slovenia, will be discussed at a meeting of UEFA's national teams competitions committee on 11 May, for ratification at an executive committee meeting on 27 May.
UEFA has also moved to ease the financial pressure on European clubs caused by the coronavirus pandemic by releasing €70m worth of benefit payments related to Euro 2020 immediately.
The governing body announced that €50m will be given to clubs that released players to the 39 countries that did not qualify for the delayed finals or reach the play-offs.
A further €17.7m will be given to clubs that released players during regular qualifying to the 16 countries which will take part in the play-offs, while €2.7m will be distributed upon completion of the matches in the autumn in respect of players being released to play in the play-off matches themselves.
The payments were originally due to be made upon completion of the play-offs, which had been scheduled for March prior to the Covid-19 outbreak.
The payments will range from €3,200 up to €630,000 and will benefit 676 clubs in total across all UEFA's 55 member countries.
The Republic of Ireland were due to play Slovakia in a Euro 2020 play-off semi-final on 26 March Having being initially pushed back until June, that game will most likely now take place in October.