Manchester United scouts reportedly watched William Carvalho and Joao Mario play for Sporting Lisbon in their 1-0 victory over Moreirense on Saturday.
According to the Sun's Andrew Richardson, the Red Devils have been eyeing central midfielder Carvalho "regularly" in recent years and are looking to make changes for next season.
Richardson added midfielder Mario has only emerged as a United target "in recent weeks."
Both could be decent additions for United, who look set for another busy summer following a poor 2015-16 campaign under manager Louis van Gaal.