St. John Damascene is frequently brought up in the filioque debate. Edward Siecienski recounts in his excellent book that Damascene's statement that only the Father is Cause of the Holy Spirit was the primary stumbling block for the Greek delegation at the Council of Florence.
Damascene's views on the procession of the Holy Spirit are subtle, but it is clear from a number of places in On the Orthodox Faith that he understands the Holy Spirit to proceed from the Father through the Son. Indeed, he says this explicitly. Of course, some people might interpret this procession through the Son as a merely "temporal" procession.
However, what is less often noted is Damascene's teaching in his somewhat less accessible work, On Heresies. If I recall correctly, it received no mention in Siecienski's book, but it is important for making clear that Damascene's procession through the Son is not merely in the temporal sphere. At the end of the work, he gives a creedal statement explicating the main dogmas of the orthodox faith. Here is the relevant passage:
Think of the Father as a spring of life begetting the Son like a river and the Holy Ghost like a sea, for the spring and the river and the sea are all one nature. Think of the Father as a root, and of the Son as a branch, and of the Spirit as a fruit, for the substance in these three is one. The Father is a sun with the Son as rays and the Holy Ghost as heat. (St. John of Damascus, On Heresies, 103)
While this makes it clear how the procession is certainly through the Son, clearly, the river plays a role in the production of the sea, the branch plays a role in the production of the fruit, and the rays play a role in the production of the heat. In other words, the Son plays an intrinsic causal role in the production of the Spirit. On the other hand, from this analogy one can easily discern a sense in which only the Father is the cause of the Spirit.
This is the same as what Latin theology says, and in fact these analogies are almost identical to those given by the Latin writer Tertullian, who says explicitly that the Holy Spirit proceeds through the Son and is clearly referring to the eternal relations in the Trinity. (See Against Praxeas Chs. 4 and especially 8 for the analogies.) Indeed, I wouldn't be surprised at all if Damascene's original source for these images ultimately traces back to Tertullian.
The issue is that the Greek Fathers mean by "proceed" and "cause" to also include the fact that the Father is the Source of the entire Trinity, including of the procession which happens through the Son. Whereas the Latins have a more minimal conception when using the word "proceeds," and are merely signifying that both Father and Son play some sort of causal role in the production, even though the Son's role is secondary. The Latins, after all, affirm that the Spirit proceeds "principally from the Father," as St. Augustine says. For more on this, see here. That is how St. Maximus was able to defend the Latin filioque as orthodox.
The problem is that Easterners who agree with the commonly held monopatrist view of Photius cannot accommodate Augustine or the other Western Fathers and saints, since this theory holds that the only procession through the Son is in the temporal sphere, while in the Trinity itself the Son and Spirit are like two completely separate branches from the Father, without any ontological relation to each other. There's no way to accommodate that within the Western Fathers, who already teach the filioque early on. But clearly the catholic Church cannot anathematize half of the Church Fathers. Western theology, on the other the hand, can easily accommodate the teaching of the Eastern Fathers that the Spirit proceeds through the Son, and that the Father is the source of the entire Trinity. As a number of Orthodox scholars have recognized, properly interpreted, there is not a contradiction between the Western and Eastern Fathers' views on the Holy Spirit's procession.