The Times, as quoted by the Daily Star, is reporting that Manchester United are interested in a deal to sign the 21-year-old this summer.
The same article states that the Red Devils are ready to launch a £30m to sign the English midfielder in the current transfer window.
According to the story, Manchester United are confident the sum will tempt Newcastle into selling Longstaff.
But the report suggests the Magpies will hold firm and refuse to consider the sale of their home grown talent this summer.
Longstaff signed a new contract with Newcastle in December that will run until the end of the 2021-22 season.
The Newcastle star’s situation at St James’ Park appears to be in doubt after manager Rafael Benitez parted company with the club last week.
Benitez was responsible for giving Longstaff his big break in the Newcastle team.
Although the 21-year-old was a first-team regular under the former Liverpool FC manager to see his stock rise, Longstaff could be deemed surplus to requirements under his replacement.
Manchester United have already signed two British players this summer after they recruited Swansea midfielder Daniel James and Crystal Palace defender Aaron Wan-Bissaka.
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