Longstaff has been linked with a move to Old Trafford for weeks now.
The 21-year-old enjoyed a breakout season last term, after arriving back from a full year on loan in League One with Blackpool.
Longstaff went on to tie down a regular spot in Rafa Benitez’s first XI in January and February, starting eleven consecutive matches.
But his season was cut short by a knee injury he sustained against West Ham on March 2.
Now though, Longstaff has returned to pre-season training fitter than ever.
But he is sure to have been heavily distracted by interest from Premier League giants United.
With Red Devils boss Ole Gunnar Solskjaer looking to attract the best, young British talent, Longstaff is understood to be a primary target for the Norwegian.
However, after showing glimpses of real promise, the Toon have no plans to sell him, and are keen to make him a key part of their long-term plans.
But it might not be that simple for Newcastle.
According to Sky Sports, Longstaff wants the chance to speak to United to discuss a potential move.
The Red Devils are sure to give the central-midfielder a bumper pay rise, as well as offering him the chance to play European football.
Should St James’ Park bigwigs be unwilling to open that door though, Longstaff will accept their decision.
He is understood to be fully committed to Newcastle, and is not expected to force a move at this stage.
Another potential snag in the deal is the transfer fee for Longstaff.
United are thought to value the youngster at around £20m.
However, having seen them fork out £50m for 21-year-old right-back Aaron Wan-Bissaka recently, Newcastle are reportedly demanding a similar amount.