Ronaldo came on just before the hour with United leading 1-0, but Everton equalized in the 65th minute and held on.
In a video posted on social media, Ferguson is heard telling Khabib Nurmagomedov, a great mixed martial arts artist, that Everton received a boost “when they saw Ronaldo not playing …”
When Nurmagomedov reminded Ferguson that Ronaldo came into the second half, the Scot added: “Yes, I know … but you should always start with your best players.”
Ronaldo has said that Ferguson, who first signed him as an 18-year-old from Sporting Lisbon in 2003, played a major role in the player’s return to Old Trafford.
United, who have 14 points in seven league games, will face Leicester City on October 16 in the next round of matches after the international break.