Help pest or mesophyll collapse?

[LizB88]

Hello, I'm new member, I'm not new to having orchid, but still a novice. I need help identifying and treating one of my new orchids. I got this Pahl at a discount from a florist ($5.00) because the flowers stem was broken. After using florist tape on the stem, the flowers open, and they look great. However, when cleaning the leafs, I notice the underside of one of the leaf to be damage. This is the only leaf, but I don't know what could it be. I thought that maybe mesophyll collapse, but I thought that would show on the upper part of the leaf.
Thank you for all your help.