I checked the UEFA regulations and there is no reason why he shouldn't be on List A. Since we have only 2 club trained players (4 is minimum) we were forced to reduce the A list from 25 to 23, but even that way, we could have excluded any other player, yet we chose Lichtsteiner.
Why? Bentancur and Sturaro were much more logical choices. Or Asamoah/De Sciglio.
The only logical reason I can think of is that we have some deal to sell him in January to a club playing in this year's group stages. If we registered Licht for the group stages, he'd have became automatically ineligible to play for another team in CL.