In my opinion it shouldn't be allowed. Unless it's in a competition that the athlete's team in question isn't playing, in that case, I don't see any problems.
I think that it is impossible. this will create a lot of precedents. football players are friends with each other, for example, playing for the team of their country. they will simply gather into a pool and will break through the results with a high probability, precisely blocking the margin of the offices in their favor, having insider information.
and in general, such a resolution is bad for any sport.
Arent there some rule btw which prevents any Premier League player actually doing that ?!? Ofc if someone is stupid enough to do it then they probably will find some illegal way for it (for example setting up account in someone else's name or whatever) ...