Schumacher, however, denied favouring his friend over the similarly Mercedes-powered Hamilton, while a McLaren spokesman agreed "There is no conspiracy".
But Hamilton has now accused Toro Rosso duo Jaime Alguersuari and Sebastien Buemi of letting fellow Red Bull stablemate Vettel easily pass last weekend before getting in his way.
"Definitely there was some of that - all of a sudden moving in my way - which caused a bigger gap," the Briton alleged. "I hope the stewards are aware of it."
According to the Telegraph, Red Bull boss Christian Horner answered "no way" when asked if Toro Rosso is playing tactical games on the senior team's behalf.
A Toro Rosso spokesman added: "The suggestion we would have held up any other car to favour a Red Bull is preposterous, and would never have happened."
Hamilton, meanwhile, said audaciously before Monaco that if he was sitting in a Red Bull this season, he would be quicker than Vettel.
And Bild newspaper published comments by Hamilton claiming he "works on a higher level" than Vettel, and insisting that "the only one who can beat him is me".
"I guess Lewis said it all," responded Vettel in an interview with F1's official website. "If that is what he thinks, that's fine with me."