it just makes my heart hurt ...

I err on the side of caution. This I know. I laugh at myself sometimes.

"I'd love to enter the trial in a month but Sally was sore a year ago at that time so I won't."

"I volunteered to work and Sally will be too stiff if she sits in a crate for the day - even if it would be after her classes"

"Oh Harri horse looks a little stiff, we'll go for a walking hack instead of the ring work we had planned."

"Oh you didn't leap up when I put my shoes on, perhaps you aren't in the right head space to learn something new - lets reinforce what you do know"

and so on ...

That said I am pretty sure my animal gang would pick playing  training here over some of the other options. Many years of listening when I see an animal in discomfort have left me with some doozy statements that rattle around my head at times.

"He's old, I want to show. What if he is never sound again?"

"She's not really lame, just uncomfortable"

"Do you think it's painful? Couldn't it just be mechanical?" (and the answer to that - no matter the species in sudden onset change of gait is a BIG RESOUNDING NO)

and so on and so on ... right down to "I can't see it" (umm playing ostrich helps no one here)

I am sorry if it was the only show you had planned. I'm upset for you if it is the only show you can get to in two months. I understand the devastation of withdrawing if it's a title on the line. Really, truly, I am and I do.

Seriously though there are so many reasons to respect what your animal's body is saying and NOT trial or show if you suspect or see pain or discomfort anywhere.
1. Your animal partner plays the competitive version of your sport for you. They would have just as much fun playing at home when conditions were perfect and you were in the best mood. We have a HUGE responsibility to consider their interests. And I'm going to take that further and add ahead of our own. That's right. We control what we do as a team therefore the onus is on us to make the experience as positive, stress free and painless as possible for the animal half of the team. (If we can do it for us too all the better!) They TRUST you to make the right call for them.
2. You may make things much much worse by pushing through it, whatever "it" is. That is not OK. (be grateful that's as much as I'm saying on this one)
3. If your animal is painful they cannot be themselves. Maybe they will be worse; maybe they will be better but either way it's not a true testament to the state of your partnership.
4. People who are new to a sport, or young, are looking around and up to everybody. What kind of example does it set if you will show a sore or sick friend? Don't be bitching to me about them or anybody else when they bring their dog with worms or that was exposed to kennel cough, or their lame horse to the next show if you are demonstrating less egregious examples of trialing animals not in top form.

I had a nice conclusion written up - I erased it to leave you this thought. If it feels at all wrong, At all like you are pushing it, if somebody else can see your dog or horse is not Quite Right if you get that sinking oh dear feeling .. even if things are  not absolutely clearly WRONG please let them stay home and recover well and wholly. Please. You make my heart hurt when you don't.

At the very least think about it.