Ole Gunnar Solskjaer is growing frustrated at the slow progress in his summer rebuild.
United are desperate for fresh faces this summer and have so far brought in Daniel James and Aaron Wan-Bissaka.
Solskjaer had hoped to bring in a number of signings ahead of next season, with a need for added depth in defence and midfield.
Longstaff is being targeted after a promising campaign with Newcastle last term.
The 21-year-old is reportedly keen on a move and according to the Evening Standard, he had hoped to join United ahead of their pre-season tour to Australia.
The Red Devils flew out last weekend and they’re taking on Perth Glory tomorrow.
But a move for Longstaff hasn’t materialised, with Newcastle playing hardball over the fee.
Reports earlier in the window suggested the midfielder could be available for £25m.
“Longstaff had hoped to join United ahead of their pre-season tour to Australia.”
However, with the club currently without a manager, and a growing need for new signings themselves, Newcastle are believed to be demanding £50m.
United also want a new centre-back, with Leicester’s Harry Maguire still their No.1 target.
But the Foxes want £90m, which Ed Woodward is reluctant to pay.
The Evening Standard claim Solskjaer wants at least two signings before the season starts.
Yet with Romelu Lukaku and Paul Pogba heavily linked with exits, that number could increase.
Solskjaer remained defiant when quizzed about the high transfer fees being quoted.
“We’re Manchester United. We don’t have to sell and don’t have to overpay,” he said.
“You have to have the right players at the right price.”