The Red Devils are also said to be monitoring the progress of Richarlison, who netted 13 Premier League goals in his debut season at Goodison Park last term.
Speaking on the subject of United's interest in Richarlison, Silva told Manchester Evening News: "I believe it is not just Manchester United. I believe it is some more. As a club we have to keep our best players."
United came under considerable criticism for failing to improve their options up front over the summer after dispensing with Romelu Lukaku and Alexis Sanchez.