The Red Devils are said to have opened talks over a possible swoop for the 22-year-old.
While reports have claimed that United are unwilling to meet Carvalho's release clause, which is thought to be in the region of £37m, Ignacio has stated that the Portuguese club do have replacements in mind.
"It's not like the old days when players left Sporting at any price," Ignacio told the club's TV channel.
"We are not concerned with William Carvalho because we have alternatives, who will want to play as well. The termination clause ensures a great deal to Sporting. I am very pleased with the negotiations."
Carvalho has also been linked to Juventus and Real Madrid.