Do you still have an avatar pool ? is your citadel dilapidated? if so then this is the reason why you are missing the avatars. And provided you meet upkeep this week, then the avatar (s) should appear back in the pool at your next build tick.
If your citadel hasn't dilapidated then it could be a bug. What does your clan notice board say about the avatar ? are you playing in NXT?
Valravnsaid: Umm, what do you mean by dilapidated? So, if my citadel does not meet the upkeep this week, the avatar will disappear from the pool this week? Yes, you need to meet weekly upkeep to maintain use of Clan Avatars.
Dilapidation just means that your Citadel is in a "broken" state for missing upkeep during a given week. You should notice a gloomy atmosphere with torn flags in your Citadel along with a slight color change to everything.
Your Avatar will return after the next build tick where upkeep has been met.~ Sicariu