Don't spar then.

Many places wouldn't accept that. Do you just sit out that section?

They may say "come on, we'll go easy, it's not a big deal" but they won't force you or something.

But if they do, or if they give an ultimatum,then those places/trainers suck. If you have valid reason to not spar and they still say "come on" leave the gym because it's not healthy.

My place did suck then. And I did get hurt..

Usually the gyms I've been to, they spar only a full day/week so I just don't show up that day. Other times I just sit out and watch. Though that only happens when I don't want to, I've sparred many times.