Four Norwich City players could represent their respective nations in the October international break.
Grant Hanley (Scotland), Wes Hoolahan (Ireland), Michael McGovern (Northern Ireland) and Angus Gunn (England Under-21s) are all in line to feature for their respective nations.
Marley Watkins (Wales) had initially recieved a call-up, but has subsequently withdrawn through injury.
Gordon Strachan's side are likely to need a maximum haul from those two matches in order to keep their hopes of reaching next summer's tournament alive.
The Republic of Ireland need similar results, with their first of two games being a Group D meeting at home to Moldova on Friday, October 6 (7:45pm).
They then take on Wales in Cardiff on Monday, October 9 (7:45pm), with Watkins having pulled out of the Welsh squad with injury.
There is less immediate pressure on Northern Ireland, who have already secured at least a play-off spot after a superb campaign in Group C.
McGovern's side still have a very remote chance of topping the group, but will need to overcome heavyweights Germany in Belfast on Thursday, October 5 (7:45pm) to keep those hopes alive.
Northern Ireland would then need to win in Norway on Sunday, October 8 (7:45pm) while hoping Germany don't collect a probable three points at home to Azerbaijan on the same night.
Finally, England Under-21s face European Championship Qualifiers at home to Scotland on Friday, October 6 (6pm) and away to Andorra on Tuesday, October 10 (6pm).