Depending on the temperature, the axolotl can go fine with out food for a lot longer than a week. So a week without eating does not by any means indicate starvation is imminent. Still your concern is valid, and I would continue to attempt to feed it. If you're really worried, separate the axolotls. I once had a problem where one newt ate all of the food before the others could get to it, this can happen and may not even be very obvious. Even if aggressive tank mates are not the problem, separation can still help you monitor the one who isn't eating better. If it starts to look scarily thin you might want to try force feeding, but this is a last resort.