Man City and Man Utd's dreams of European success this season have been dealt a blow following the government's announcement regarding quarantine measures in the UK.
From June 8 anyone entering the UK must isolate for a minimum of 14 days as a safety precaution against the threat of another coronavirus outbreak.
That could scupper any plans UEFA have to get the European club competitions up and running again in the coming months.
City are leading their Champions League last-16 tie with Real Madrid after a momentous win at the Bernabeu, while United have one foot firmly in the quarter-finals of the Europa League after a crushing 5-0 defeat of LASK.
Various stakeholders in elite sports tried in vain to contest a two-week quarantine, but to no avail.
Culture secretary Oliver Dowden had been fighting their corner, but sports stars have not been included in a list of exemptions from the quarantine.
Real Madrid were due to fly into Manchester for their second leg with City back in March until the clash was postponed just days before as the coronavirus outbreak began to accelerate.
Under the government guidelines, should Madrid now return to the UK for the match, all of their players and staff would be forced to self-isolate for 14 days prior to the fixture, making it almost impossible to fit into the already packed football schedule.
The ruling would also affect Chelsea who are due to travel to face Bayern Munich for their second leg, though Frank Lampard's men already have a mountain to climb as they trail 3-0 from the first leg.
UEFA have previously suggested proposals to hold mini tournaments in one nation involving the final four teams of each competition, though they were hopeful of concluding last-16 and quarter final ties in normal venues behind closed doors before then.
Istanbul was mooted as a potential location for the prospective tournaments in August, given the Turkish capital was due to host the Champions League final before the pandemic, though nothing has yet been confirmed.
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