The Circle of Spores Druid feature Fungal Infestation states:
If a beast or humanoid that is Small or Medium dies within 10 feet of you, you can use your reaction to animate it, causing it to stand up immediately with 1 hit point. The creature uses the zombie statistics. It remains animate for 1 hour, after which time it collapses and dies.
Circle of Spore druids also gain access to the Gentle Repose spell, which states:
You touch a corpse or other remains. For the duration, the target is protected from decay and can’t become undead. The spell also effectively extends the time limit on raising the target from the dead, since days spent under the influence of this spell don’t count against the time limit of spells such as raise dead.
There seem to be some good arguments that they cannot work together:
- First, Gentle Repose states the target cannot become undead, which would seem to preclude Gentle Repose working on a fungally infested creature that appears to be in some sense raised from the dead.
- Second, gentle repose states you touch a corpse or other remains - one could argue that using the zombie statistics, the fungally infested entity is neither a corpse or remains, but an undead zombie.
However, there are also some reasonable arguments that they could work together:
- First, the Fungal Infestation does not say that the creature is undead or a zombie, but that it uses the statistics of a zombie, which might leave room for a RAW interpretation that the features could work together (for example, it could be considered a fungally infested corpse or fungally raised remains).
- Second, Gentle Repose says that it extends the time limit of raising the target from the dead and makes reference to spells like Raise Dead, which in flavour are similar to what happens with Fungal Infestation.
RAW, can a player cast gentle repose on a zombie created by Fungal Infestation?