The midfielder, 21, has been in fine form for the Magpies in recent weeks and it is understood his performances have not passed Aidy Boothroyd by.
According to the Chronicle, the U21s boss is 'well aware' of the academy graduate and is keeping a close eye on his progress.
Longstaff made the bench for six Premier League games before finally being handed his top-flight debut on Boxing Day, coming on in the 4-0 defeat at Anfield.
But he has played the full 90 minutes in the last four games, including the 2-1 win over Manchester City on Tuesday, and scored his first Newcastle goal in the FA Cup win over Blackburn.
Longstaff was one of the standout players for Rafa Benitez's side in the game and was the player who pick-pocketed Fernandinho before being tripped by the Brazilian for the penalty which Matt Ritchie dispatched.
In a recent interview with Sky Sports, the midfielder said: "It's been great to play against the top teams in the world, it can only benefit me.
"As a 21-year-old lad, from last year watching them on the telly, to this year being up close and personal with them, it's a little bit surreal, but I think it's something that I try to take in my stride.
"Sometimes you do look around and think: 'How has this happened in such a short space of time', but I'm loving every second of it."
The Young Lions are next in action in March when they take on Poland at Bristol City's Ashton Gate and then current Euro U21 champions Germany at the Vitality Stadium, home of Bournemouth.
Boothroyd will be hoping they can go further than the 2017 U21 Euros – when his side lost to Germany on penalties in the semi-finals – in Italy and San Marino this summer.
And with Lewis Cook likely to miss the tournament as he continues his recovery from a ruptured anterior cruciate ligament suffered in December, a space in the midfield may well have opened up for Longstaff.
His performances on loan at Blackpool last year alerted Ireland and Scotland checked his family history to see if he could represent either nation.
But the North Shields-born ace is only eligible for England, which would no doubt be welcome news for Boothroyd.
Level-headed Longstaff rebuffed any suggestions that he might get ahead of himself with his current rise.
He added: "It wouldn't be right for me to get above my station when we're in the position we're in.
"There are enough strong people around me, particularly in the dressing room, that wouldn't let it happen.
"As much as it's going great at the minute, it just takes one thing for it to start going the other way."
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