Hi, are you using any kind of fertilizer? Yellowing can mean overwatering, but it can also mean chlorosis, which is not enough of certain trace elements or light. If your plant is not in the most sun you can give it all day long, and you haven't fertilized (with one meant for cacti/succulents) then it's certainly time to do so.

As you took off this leaf 2 days ago, I'm assuming it doesn't have roots, so it won't need fertilizer, or even water, yet. I suspect this leaf was dying when you pulled it, and I don't hold out much hope for it. The quickest way to propagate your Sansevieria is to divide the current plant, although you will have quicker success in the Spring.

I wouldn't fertilize now either. I agree rooting in spring has its benefits, but since you're trying to save the leaf at this time, you can't hold off till spring..
Like Rjm stated, diving the leaf is one way to root. Actually, I've seen pics of how rooting Sans is done..One leaf is cut into 2-3" pieces, set upright/angle in well-draining soil. The problem is, since your leaf is yellow, which normally happens when Sans are over or underwatered, this leaf may not root..When rooting, heatlhy foliage is recommeded..Neither the oldest nor youngest leaves are advised.
I'm not saying your leaf is unhealthy, since it's still firm (no rot, right?) So, it might have a chance of survival with some work. It's also a good experiment.
I wouldn't use the entire leaf to root. You've a better chance at success cutting into pieces. If you decide to go this route, there's no need for plastic (humidity) In fact, you want the soil to dry out to a degree, adding plstic will keep soil too wet. The best container is a small, shallow dish/tray. Set cuttings a few inches apart. Place tray in medium light (no direct sun) If you use Superthrive Hormone and Vitamins, add a small amount once a month..If you don't have/use Superthrive, perhaps a light dose of Fish Emulsion will help..a very light dose. Good luck, Toni

I wouldn't hold much hope for the yellow leaf, it's dying, not good material to start new from & likely won't work (sorry). But can't hurt to try.

I'm guessing this was one of the lower, older leaves & it just naturally aged out.

Yellowing leaves on a Sans, (as said above) are often from overwatering; IME, underwatered tend to dry & shrivel.

I gave a talk on Sans. to my local Indoor Gardening Society couple of yrs. ago. I grow abt 10 diff. kinds (lately few are IDed). I say all this to say, IME the less one does to these plants the better they'll do. I wouldn't bother w/ most amendments for Sans., they don't need it & don't seem esp. helped by them.

I would go along with the suggestion that it is probably dying from too much something. I would do nothing, no water or amendments, moderate indirect light, warm but not hot. Wait months before tossing unless the leaf gets soft. I forgot one left on a water heater in a mud room for the entire winter, in the spring it produced a pup.