Could be simple heat damage. Did it get very hot where this plant is located? If it is heat damage, it will take the leaf eventually. For some reason it takes several days for cattleya leaves. We recently had a fan go out in our greenhouse and the temps got up over 140 degrees before we were able to start cooling things down. We lost several oncidiums, paphs, and phals. I thought the cattleyas were going to be okay since they looked fine for a few days, but then many of them started showing heat stress.
As long as the new growth on your cattleya is not doing the same thing as the other leaves, it is not a virus.