You are right with ‘Client potentiel’, which literally translates to potential customer.

You could also use ‘prospect’, both would be very acceptable in a sales context.

To add something to @Nickstoy client potentiel correct answer.

As commented @Random, in linguee, you can find usages of :

• “potentiel de vente”
• “perspective de vente”

which both translate the fact the term prospective, in your definition, is not 100% sure + represent an action of a consumer and not directly a consumer itself.

You can also find “piste de vente” or “manifestation d’intérêt” which will be understood but I do not think these are business vocabulary.