The Zohar literature, including the Zohar, Zohar Hadash, and the Tikkunei HaZohar – along with their respective books and sub-divisions – was published over the course of almost 300 years (approx. 1300-1587 CE) and straddles the periods of the late rishonim and early aharonim; with the era of the former generally held to have been during the 11th to 15th centuries, and that of the latter from the 16th century until the present time.
Although there was much written on the subject of the Zohar and the authenticity of its content, only a minority of what is extant was authored in the narrow window between the publication of the Zohar literature and the end of the period of the rishonim. Much of what exists in this genre was written in the period of the early aharonim and remains very valuable to anyone engaging in a historical study of the Zohar. The main reason for the lack of earlier literature is that the Zohar, even after its initial publication, was not a very widespread or well-known book.
What is available exists in two types:
 independent works authored specifically on the subject of the authenticity of the Zohar literature, and  quotes from Hazal, geonim, and rishonim (e.g. Rasag, Rashi, Tosafot, Rambam, et al) whose explicit statements in times prior to the Zohar are directly contradicted by, and in many cases preclude, explicit statements made later by the Zohar and its commentaries.
Works in the period of the [later] rishonim which dispute the Zohar and its authenticity:
- Sefer Behinat HaDat – Rav Eliyahu Del Medigo (15th Century CE)
- Sefer HaYuhasin, account of Rabbi Yitzhak de-min Akko – Rav Avraham Zakuto (15th Century CE)
Works in the period of the aharonim which dispute the Zohar literature and its authenticity:
- Sefer Ari Nohem – Rav Yehudah Aryeh DeModena (17th Century CE)
- Mitpahat Sefarim – Rav Yaakov Emden (18th Century CE)
- Shu”T Hatam Sofer (6:59), referring to the work of Rav Emden – Rav Mosheh Sofer (18th Century CE)
- Teshuvah Me-Ahavah (1:14) – Rav Eli`ezer Fleckeles (19th Century CE)
- Milhamot HaShem – Rav Yihya Shelomo Al-Qafih (19th Century CE)
These are by no means exhaustive lists, but they do comprise the majority of what is available.
The following are examples of literature prior to the publication of the Zohar which discuss similar topics:
- HaNivhar Emunot ve-Deot by Rav Sa`adyah Gaon (10th Century CE) – This work is a comprehensive compendium of explanations that not only sets forth the hashkafah of Torah Judaism on many topics, but also includes the arguments of detractors and the basis for their being rejected. The interesting thing about this work is that it deals with almost every major theme which was to emerge under the later “Kabbalah” which became embodied in the Zohar literature – and it roundly rejects them as not being authentic or based in Hazal. These topics include the idea of multiplicity or aspects as relates to the One Transcendent God, Reincarnation, and Emanation (atzilut אצילות), among others.
- Moreh HaNavokhim by Rav Mosheh ben Maimon (Rambam – 11th Century CE). THis work details the necessity of intellectual and rational approaches to the Torah and the Prophets, as well as explaining the meaning of many mitzvot and the various reasons behind them. It also deals with concepts which were later embodied in the “Kabbalah,” such as “secret” mystical names of God and amulets, which are roundly rejected as superstitious, idolatrous, and foolish.
- Ma’amar Tehiyat HaMetim by Rav Mosheh ben Maimon (Rambam – 11th Century CE). In the first section, the Rambam accounts for the misunderstanding of his own teachings regarding the resurrection from the dead by bringing an example of a gross misunderstanding of God’s own words in the Shema (Devarim 6:4). He refers to the “belief of the dualists” who believe that the three mentions of the Divine Name in the Shema (i.e. HaShem, Elohenu, HaShem) are three separate forces/entities/modes of the Divine (halilah) that supposedly comprise some sort of composite unity. The Rambam flatly rejects this reading of the Shema in his statements there. However, the Zohar (2:53b) espouses just such a nonsensical interpretation. Ironically, this passage was used by later Christian Hebraists, and even the Catholic church, in justifying the supposed validity of their belief in a “Trinity” from “Jewish” teachings.
- Rashi and Tosafot on b.Megillah 9a (11th, 12th-13th Centuries CE). In an interesting passage about the request of King Ptolemy (Talmai HaMelekh) that the hakhmei HaSanhedrin write for him a copy of the Torah in Greek, the Gemara explains that several deliberate changes to the text were unanimously made by them during their translation in order to avoid certain polytheistic errors by Greek readers. Two of the notable changes were made in Bereshit 1:1 and 1:26 – the former being that instead of the text reading “Bereshit bara Elohim” they wrote “Elohim bara bereshit,” and the latter being that in place of “Na’aseh adam” they wrote “E’aseh adam.” In the first instance – since syntax in the Greek language often puts the most important noun in the sentence first and sorts out the meaning and parts of speech via case endings – the hakhamim did not want the Greeks to think that “Bereshit” was the name of one deity which created a second deity named “Elohim” (halilah) and that there are thus multiple powers in Heaven (halilah), so says Rashi. The Tosafot add to this by saying that “Bereshit eino shem kelal ela ba-tehilah” meaning that the term “bereshit” is not a name at all, but is rather just the Torah’s way of saying “In the beginning.” The second change was made due to the presence of the plural form (i.e. “Let us make man”), lest again the Greeks think that the Torah promotes polytheism and that multiple gods created mankind (halilah – see Rashi there). However, the Zohar – in commenting on these very passages – adopts the mistaken and erroneous views which these changes were specifically intended to negate. On Bereshit 1:1 the Zohar says that “Reshit” is the name of a partzuf/sefirah and it creates/emanates another partzuf/sefirah named “Elohim” which it can then inhabit. On Bereshit 1:26, the Zohar depicts two of the partzufim (faces/personalities which supposedly make up the Divine), “Abba” and “Imma,” arguing whether or not they should make man – “Abba” is con while “Imma” is pro – and in the end “Imma” says that although mankind will sin against us “Let us make man” anyhow. The implications of these interpretations in light of the Gemara and its commentators are both shocking and wide-reaching.
There are many more things which could be listed here, but much of it is already written in the works mentioned above.