Could a land vertebrate re-evolve gills after moving back into the water?

I know there are examples of land vertebrates moving back into the oceans, such as in the case of whales, and marine reptiles, but in every case that I know of when a land vertebrate moves back into the water it continues to breath air, and come back up to the surface to take a breath.

Could a land vertebrate re-evolve working gills after migrating back into the water, and if so what types of evolutionary pressures might cause a land vertebrate to revert back to breathing water instead of air?

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Could a land vertebrate re-evolve gills after moving back into the water?

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