Rangers have 48 hours to complete the Carlos Pena and Eduardo Herrera for their first round Europa League clash on June 29.
The Mexican duo jetted in for contract talks a fortnight ago with fees apparently agreed for both players to move to Ibrox with Alfredo Morelos also lined up from HJK Helsinki.
All three players require work permits and visas to work in the UK with the process appearing to be slow and drawn out for the Sevco applications.
Unless the three players appear on Monday with the documentation they will miss the deadline for the Europa League qualifier although one player can be added 24 hours before the first leg.
After agreeing a deal with Krasnodar for Eboue Kouassi in January Celtic had the paperwork completed within five days allowing the midfielder to train with his new team mates in Dubai.
The delay in the Sevco deals could be down to a number of factors but if the transfers fail to go through on Monday Pedro Caixinha will have just four new faces for the Europa League first round tie with Bruno Alves in the Portugal squad at the Confederations Cup.