The Telegraph is reporting that Ole Gunnar Solskjaer has set his sights on a potential deal to sign the 21-year-old to bolster his midfield this summer.
The same article states that Manchester United executive vice-chairman Ed Woodward has already contracted Newcastle managing director Lee Charnley to ask about Longstaff.
According to the same story, the 20-time English champions are prepared to pay between £18m and £20m to sign the Newcastle youth graduate in the summer.
The Telegraph go on to report that Manchester United have been left stunned by Newcastle’s £50m price tag for the central midfielder.
Manchester United have already signed two new players in the summer transfer window as Solskjaer looks to improve his squad ahead of the new season.
The Red Devils started their summer spending with the £15m addition of Daniel James from Championship side Swansea City, before landing Aaron Wan-Bissaka from Crystal Palace.
Solskjaer took over the reins from Jose Mourinho back in December after Manchester United made a disastrous start to the 2018-19 season.
The Red Devils appointed Solskjaer as their permanent manager at the end of March but Manchester United could only muster a sixth-placed finish.
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