There is a new paper on investor presence in European football leagues and competition available:

Based on a hand-collected dataset on investor cash flows to more than 300 football clubs, we examine the impact of investor presence on competition in major European football leagues. By spending investor cash flows on more valuable players, clubs with investors on average become more successful. Thereby, increased investor presence results in reduced competition within national football leagues in Europe. However, investor presence also leads to greater international success of the respective football leagues as approximated by UEFA prize money and annual UEFA country coefficients. Softened UEFA fair play regulations to attract more investors are thus likely to reduce competition within national football leagues.

The paper can be downloaded here.