Manchester United has reportedly been informed by Sporting Lisbon that Joao Mario will only be sold this summer if his buyout clause is being met.
Recent speculations suggest that the Red Devils have sent scout to monitor the winger on numerous occasion.
According to A Bola, United have since firmed up their interest by beginning transfer negotiations with their Portuguese counterparts.
However, the report added that the lions are not prepared to dislodge from their price, which is the £47m buyout clause in his contract.
The 23-year-old, who has scored seven goals in all competitions this term, is expected to feature for Portugal at Euro 2016.