Townsend features in England's provisional squad for the upcoming European Championships, but along with his Three Lions teammates is not due to report for training until Wednesday.
And the 24-year-old has allegedly used the break to discuss a move to the Portuguese runners-up, with Record reporting he will undergo a medical, according to the Sun.
Townsend arrived at St. James' Park for £12 million in January and scored four goals in 13 appearances, though it wasn't enough to spare the Magpies the drop.
However, it is claimed by a separate Record article that the former Tottenham Hotspur winger has a clause enabling him to leave the Tyneside club for €10 million (around £7.7 million).
Townsend's former White Hart Lane teammate Sandro, who spent the latter half of the campaign on loan to West Bromwich Albion, is said to be closing in on a move to Sporting himself.
"Sporting would be a great opportunity," the Sun quotes the Brazilian as saying.