The continent's top club competition is in the spotlight like never before after Saudi teams shelled out on the likes of Cristiano Ronaldo, Neymar and Karim Benzema.
The round of 16 began on Tuesday last week, three days after the final of the Asian Cup, which was won by hosts Qatar.
The Asian Football Confederation (AFC) is responsible for both competitions, which span a vast area from Australia to the Middle East and Central Asia.
The current Champions League is split into two zones, "West" and "East", until a two-legged final home and away.
Starting in the next campaign, there will also be a geographical split at the start of the tournament, but the quarter-finals, semi-finals and final will be held in Saudi Arabia.
FIFPRO said this remodelled version, which will see the winner take home an increased cheque of £9.5 million, was also unsustainable.
Takuya Yamazaki, FIFPRO's chairman for Oceania-Asia, hopes its report will "spark meaningful discussions with governing bodies, leagues, clubs and fans" about the Champions League.
"The results indicate that, as anticipated, the merits do not outweigh the drawbacks for most players and clubs, making it an unsustainable system," he said in the report.
FIFPRO accused the AFC of adopting "a top-down approach that excludes the voices of players and clubs from decision-making".
It called on the AFC to forge "a genuine partnership with players, clubs and leagues to ensure that the competition delivers for all parties".
Among its conclusions, the 49-page report said that the average quality of teams in the Champions League was inferior to the top domestic divisions in Japan, South Korea and Saudi Arabia.
It said the average quality of the competition was also going down.
FIFPRO also voiced concern about the economic cost for teams, given the long travel sometimes involved, and the effect of travel and match scheduling on the workload of players.
AFP has contacted the Kuala Lumpur-based AFC for comment.
