You said it is in a large pot. If the pot is too large for a smaller plant and it just started dropping leaves, there's a chance the plant is staying soggy between weaterings and is getting overwatered. (Citrus don't like soggy feet and if there's more soil than roots they stay wet too long.)

Or if it recently had a dramatic temperature change, like sudden cold, or sudden hot, that can cause them to lose leaves, too, I think.

You didn't say what zone you're in or if you recently moved it from inside to outside... so that info would be helpful.

Have you fertilized recently?

Do the leaves look normal?

You might also want to post a picture.