Several Premier League clubs could be without key players when the first round of fixtures gets underway.
The decisions, announced by the UEFA Appeals Body, relate to incidents during qualifying matches played on July 29 and 30.
FIFA Secretary General Mattias Grafström and FIFA Management Board members have expressed their full backing for President Gianni Infantino.
UEFA has welcomed FIFA's decision to abandon plans to sell a stake in its competitions.
The sanctions follow a self-report by Chelsea's current ownership after completing its takeover of the club in 2022.