A caster T readies a spell on their turn, then an enemy caster E targets them with feeblemind. T passes the Constitution save against the 4d6 psychic damage to maintain concentration, but fails the Intelligence save and suffers the greater effects of feeblemind.
As I understand it, readying a spell casts the spell but does not release it.
Feeblemind says of the target, in part:
It can't cast spells, activate magic items, understand language, or communicate legibly by any means. However, it can identify allies, and follow and protect them.
Since T has already cast the spell while readying it, does T lose the readied spell when they are affected by feeblemind?