Manchester United have reportedly been informed by Sporting Lisbon that Joao Mario will only be sold in the summer if his release clause is met.
Recent speculation claimed that the Red Devils had sent scouts to watch the winger in action on numerous occasions over the last few months.
According to A Bola, United have since firmed up their interest by beginning transfer negotiations with their Portuguese counterparts.
However, the report adds that Sporting are not prepared to budge on their asking price, which is the £47m buyout figure that is contained within Mario's contract.
The 23-year-old, who has scored seven goals in all competitions this term, is expected to feature for Portugal at Euro 2016.
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