The Red Devils have been regularly linked with a move to sign the 21-year-old Newcastle midfielder in the summer tranfer window so far.
Longstaff established himself as a regular in the Newcastle team under Spanish head coach Rafael Benitez in the 2018-19 season.
Manchester United have made a concerted effort to sign young British talent in the summer transfer window – and Longstaff would fit the bill.
Benitez’s departure earlier this month could help Manchester United convince the Newcastle youth graduate to leave St James’ Park.
However, Sky Sports News reporter Solhekol revealed that the Magpies are determined to keep hold of Longstaff beyond the summer transfer window.
Solhekol wrote on Twitter: “There were high-level talks last weekend between Manchester United and Newcastle United about Sean Longstaff.
“Newcastle won’t confirm there were talks but we understand Newcastle categorically not interested in selling Longstaff & and see him as a big part of their future plans.”
Longstaff netted his first Premier League goal in a 1-0 victory over Burnley in February.
Manchester United started their summer spending spree with the £15m addition of Welsh midfielder Daniel James from Championship side Swansea City.
The Red Devils have also snapped up England Under-21 international Aaron Wan-Bissaka in a £50m deal from Premier League side Crystal Palace earlier this month.
Manchester United have failed to win a trophy in the last two Premier League seasons under Jose Mourinho and Ole Gunnar Solskjaer.
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