Everton have made an £8million offer for Nikola Vlasic at Hajduk Split but will face a rush to get his work permit application in place by 4pm on Thursday.
That is the deadline for clubs in the UK ahead of the window closing on Thursday evening.
The 19-year-old impressed during Everton's two-legged Europa League qualifier tie against the Croatian club but became a target for Ronald Koeman earlier this summer.
Vlasic has become a first-team star for Hajduk since making his debut as a 17-year-old and has scored 10 times in 85 appearances.