The Magpies will be participating in the Premier League Asia Trophy as they face Wolverhampton Wanderers, Manchester City and West Ham United respectively.
Longstaff is a product of the Newcastle United academy and broke through the senior team in December previous year, after having had two successful loan stints at Kilmarnock and Blackpool.
Longstaff is understood to be keen on a move to Old Trafford but Newcastle's demands mean Solskjaer's side may now have to focus on other targets.
Longstaff had hoped to be in place for the start of the tour - but a formal approach to Newcastle managing director Lee Charnley didn't come until last weekend.
Having promised major overhaul at the club this summer, Solskjaer's transfer plans are stalling as clubs demand excessive fees for key targets. And Longstaff fits into that profile perfectly, which had prompted the 20-time English champions to prepare an opening bid for the midfielder.
The Tyneside outfit have slapped an outrageous £50 million price tag on Longstaff, having seen Manchester United shell out a similar fee to sign Wan-Bissaka from Crystal Palace this summer.
Recent reports claimed that Manchester United will have to spend as much as £50m to sign Longstaff.
Leicester are demanding £90m for the England centre-back but United are hoping to strike a deal around the £75m figure that Liverpool paid Southampton for Virgil van Dijk a year ago.
The club continues to be linked with a plethora of players, largely occupying the speculated needs of a centre-back, midfielder, and potential replacements for allegedly exit-bound Paul Pogba and Romelu Lukaku.