Honorable mentions
Denis Law relegated Manchester United
Denis Law, a European Cup winner and a former winner of the Ballon d'Or, was a Scottish legend who was affectionately referred to as 'The King' by Manchester United fans. However, he is most famously remembered for 'that goal' which ended up relegating Manchester United.
Law's goal, however, was not the reason United got relegated. The goal in fact was completely inconsequential; it came in the 81st minute and didn't matter at all as United were going down regardless. A win or a draw would not have changed their fortunes, as results elsewhere had already confirmed United’s relegation.
Denis Law’s legacy will never be questioned, but it will always be marred due to that sublime back-heel goal against his former team.
Shirt sales alone pays for a world star player’s transfer fee
Despite what the internet may tell you, the money dished out on a player's transfer fee has never been recovered through shirt sales alone. Over 80% of profits made by selling shirts with the specific player's name at the back go to the kit supplier itself. This is standard for a majority of the companies like Adidas, Nike, Under Armour, etc.
The Guardian lists United's current deal as an example. We assume that the club's royalty kicks in after three million shirts are sold, and the club receives a 15% royalty on each shirt sold after that. Assuming that each shirt costs £70, then that would be £21 million made by selling 300,000 thousand shirts. United's cut from that would be a little over £3 million.
That's an insignificant amount considering that a lot of nonsense was spewed regarding Ibrahimovic’s shirt sales alone raising £50 million.