The Argentine wide-man has been one of the Portuguese champions’ key men for some time, earning much praise for his electric showings at the Estadio da Luz.
And his performances have attracted the attention of both Liverpool and United ahead of the summer.
Scouts from the Red Devils are believed to have been present to watch the Benfica man over the weekend, while Brendan Rodgers’ Reds are also keen.
Salvio is said to be locked in contract talks with the Lisbon giants to add an extra year to his current deal, but talks are on-going.
The player is believed to want his release clause of around £43.1m reduced, which is a potential issue for Benfica, who are reluctant to encourage potential suitors.