Quote:
Venues
12.07 In principle, a club must play all its matches in the competition at one and the same ground. Matches may be played either at the ground of the home club or at another ground in the same or another city within the territory of its association, or, if so decided by the UEFA administration and/or the UEFA disciplinary bodies, in the territory of another UEFA member association for reasons of safety or as a result of a disciplinary measure. In principle, venues are approved only if direct international flights and/or charter flights are able to land within an acceptable distance of the venue, in the country of the club concerned. If the match is being played in another city or country, the venue is
subject to the approval of the UEFA administration.
Alternative venues
12.08 If, at any time during the season, the UEFA administration deems that, for whatever reason, some venues may not be fit for staging a match, UEFA may consult the associations and clubs concerned and ask them to propose an alternative venue, in accordance with the UEFA requirements. Should such an association and club not be able to propose an acceptable alternative venue by the deadline set by the UEFA administration, UEFA may select an alternative, neutral venue and make all the necessary arrangements for the staging of the match together with the relevant association and local authorities. In both cases, the costs of staging the match are borne by the home club. The UEFA administration takes a final decision on the match venue in due time.
Any alternative venue has to be proposed in accordance with UEFA requirements, and one of those requirements is that the home games of any competing club must be played in a city in the territory of that club's association. If there's a suitable stadium available in Scotland - and there is/will be, as far as I understand - then Celtic's home games will be played there.