The 24-year-old, who has played a starring role in helping Cruzeiro win the Campeonato Brasileiro Serie A this season, recently claimed that a switch to Old Trafford would be a 'dream move'.
However, Mattos is adamant that Ribeiro's dream will not become a reality unless the Red Devils come up with an offer far in excess of the £6.5m fee that has been suggested by the press.
"There are no offers, just speculation," Mattos told Globo Esporte. "Everton Ribeiro said he dreams of playing for Manchester United, then people started talking, and they said he would cost €8m - that makes no sense.
"We turned down a €10m offer [from a different club] for the percentage we own and that happened halfway through the season.
"Cruzeiro don't want to let any player go. On the contrary, we want to bring in more players and that's not me talking, the president said that. Of course we are responsible, and if an absurd offer for Everton Ribeiro or any other player comes, we have to sell."
Left-footed Ribeiro, who has represented Brazil five times at Under-20 level, can operate in various positions, including wing-back, winger and central midfield.