The center panel of the predella is the noli me tangere (John 20:17). The right panel draws on the iconography of St. Mary of Egypt, holding a book and covered only by hair. The man kneeling before her would then be Zosimus. Either the artist was including the Egyptian Mary in the Magdalene's altarpiece because both were reformed sinners, or he was simply getting the two Marys confused. The latter supposition seems more likely, because the woman covered with hair in the left panel is surely the Magdalene receiving communion from Maximin, a common subject.
In any case, it is significant that all three panels feature someone kneeling. In the right panel the kneeling man models the reverence encouraged in the viewer. In the left and center panels, Mary Magdalene kneels to Christ both in the Eucharist and in the flesh.
The altarpiece photo in full resolution
The predella photo in full resolution
Also see St. Mary of Egypt
Read more about Saints Mary Magdalene, Jerome, Paula, Monica, and Augustine.