Sir Alex Ferguson fears the extinction of 'great' English clubs if the Premier League's giants join FIFA's global Super League.
The governing body is currently in discussions about the new competition - which would see clubs leave their domestic leagues to participate.
Ferguson - who managed Manchester United to 38 trophies during a 26-year stint - believes a Super League isn't an attractive option to Premier League clubs and warned that smaller teams could be forced out of the game if the new competition is implemented.
"I struggle to see why an English team would need to leave," Ferguson told the BBC.
"Without question, it is money orientated, but surely this would not be attractive to our clubs in the Premier League, which at the moment is the best domestic league in world football and is well supported financially by Sky, BT and now Amazon.
"Furthermore, the attraction of playing in the Champions League is huge for players, coaches and fans alike, as it remains the ultimate test in club football.
"A lot of clubs with great history could be lost if their partners in the Premier League upped sticks. I strongly believe this is a realistic appraisal of the value of domestic football."
Real Madrid's president Florentino Perez has had private discussions with FIFA supremo Gianni Infantino about the idea of a Super League, according to the New York Times.
However, plans for a proposed global competition are only in their infancy, with an agreement between FIFA and the clubs still a long way off.
The governing body are keen to expand the Club World Cup in 2021, from its current format of seven teams to 21 competitors - an idea that is heavily opposed by UEFA.
There has also been consultation from the European Clubs Association about altering the format of the UEFA Champions League from 2024.
The ECA plan is for the tournament to be a 32-team league, in which clubs play 10 matches against 10 different opponents, with eight teams qualifying for the knockout phase and 16 others going into a playoff to join them.
This season's Champions League has seen all round-of-16 qualifiers hail from Europe's top five leagues in England, Germany, Spain, Italy and France.
