Yoshinori Muto must wait on an FA Governing Body Endorsement (GBE) hearing to find out whether he can complete his £9.5m move to Newcastle.
The Tyneside club confirmed on Friday the 26-year-old has agreed personal terms and completed a medical ahead of a permanent switch from German club Mainz.
But Muto does not meet the automatic criteria for an FA GBE, having not played enough international matches for Japan in recent seasons, so the case will be heard by an Exceptions Panel next week.
A Newcastle statement read: "Newcastle United can confirm that Japan international Yoshinori Muto has been on Tyneside ahead of a proposed move to the club.
"An agreement has been formalised between the Magpies and Muto's current club, FSV Mainz 05, and the player has undergone a medical and agreed personal terms.
"The transfer is now subject to the player being issued with a Governing Body Endorsement, which will be determined at a hearing to take place later next week."
Muto played for Japan at this summer's World Cup, with his sole appearance in Russia coming during the 1-0 defeat to Poland in Group H.
He has scored 20 Bundesliga goals in 66 appearances since joining Mainz from FC Tokyo in 2015.