Answer:
"In the evenings he would admit privately to Clover that the hoof troubled him a great deal."
Step-by-step explanation:
Although it could possibly be the second option, in the context of the text, Clover is simply using a hyperbole to say that Boxer is working too hard. This is before Boxer is in any real danger and does not foreshadow his death.
The first option on the other hand brings worry to the reader. It brings about questions like, "Will he recover?" or, "Will he be able to continue working?". That is how we know that it is proper foreshadowing to his later demise.