Sir Jim Ratcliffe's takeover of Manchester United could in theory see them banned from Europe next season, although a solution is likely to be found.
Ratcliffe expects his purchase of a 25 per cent stake in United to be confirmed next week.
The British billionaire and his Ineos sports investment arm already own Nice, who are second in Ligue 1 and just one point behind leaders Paris Saint-Germain.
Nice are on course to qualify for the Champions League as one of three automatic spots in France, with a play-off route available to the team finishing fourth.
With United still in the hunt for a top-four finish, UEFA may have to prohibit one team on "sporting merit", leaving the team finishing lowest in their respective league out of Europe.
United could argue they remain under the control of the Glazers, with Ratcliffe only buying a minority stake, but Ineos are expected to come in to run the football operation to further complicate matters.
The only exception would allow one club to qualify for the Champions League and the other to the Conference League, with the Europa League participation blocked as the competitions are all interlinked.
Manchester City are currently in the same predicament, with sister club Girona, who are part of the 11-club City Football Group, top of La Liga.
Chelsea, Newcastle, Nottingham Forest, Crystal Palace, Brighton, Brentford, Sheffield United, and - possibly soon - Everton are all part of multi-club ownership groups.
UEFA rules currently state: "No club participating in a UEFA club competition may, either directly or indirectly, hold or deal in the securities or shares of any other club participating in a UEFA club competition."
But UEFA are expected to re-write the rule book anyway to avoid banning teams from their revamped competition next season.
A vote is not expected at the next UEFA executive committee meeting in December, but a relaxation of multi-club rules could be ratified early in January.
Aleksander Ceferin, the president of European football's governing body, hinted at changes in a wide-ranging interview with Gary Neville's Overlap YouTube channel.
He said: "We are not thinking about Manchester United only. We've had five or six owners of clubs who want to buy another club. We have to see what to do.
"The options are that it stays like that or that we allow them to play in the same competition. I'm not sure yet.
"We have to speak about these regulations and see what to do about it. There is more and more interest in this multi-club ownership. We shouldn't just say no to the investments for multi-club ownership, but we have to see what kind of rules we set in that case because the rules have to be strict."
Any club not allowed into UEFA competitions would be replaced by the next best place team, potentially earning them over £100million if they qualify for the Champions League.
