Longstaff has been linked with a host of clubs over the course of the summer as he looks to play regular first team football this season.
While clubs in the Championship are keen on Longstaff, it is Scottish outfit Aberdeen who are set to win the race for his services before the transfer window shuts.
Talks between Newcastle and Aberdeen are taking place as Longstaff edges towards a switch to Pittodrie.
Aberdeen have enjoyed a good start to the season and sit in second in the Scottish Premiership with seven points from three games.
The Dons are in action against Ross County on Sunday and it remains to be seen if they have signed Longstaff by then.
The club exited the Europa Conference League on Thursday night at the hands of Qarabag.
Aberdeen lost 1-0 away and were then turned over 3-1 at Pittodrie by the Azerbaijan side.
