My tortoise ate a very very very small amount of a mushroom and I caught him in the act and immediately stopped him I know that it was a very small amount but I’m still concerned the mushroom was red and very small
Not sure what to tell you; we aren’t entirely sure what mushrooms are bad for torts, only that tortoises may not react the same way to them tat mammals do. At least that’s the most I know.
I suggest you take your photo over to the forum that is diet specific and post the picture. There are better experts on mushrooms there. Until then, try not to panic, keep an eye on him, and give him a soak (soaking never hurts!)
In your post you say the mushroom is very small but there isn’t good context in your photo to see just how small! Can you photograph it next to a dime or other coin? Or give us a measurement.
Most likely he will be fine. If it were to poison him, it would do so quite quickly.
Most human edible mushrooms are safe. Best to stick with button or portobello mushrooms though as we know they are safe. I don't know what kind that is in your picture, but would try not to let him eat any more of it.