A druid is concentrating on a spell, and Wild Shapes. When they take enough damage to revert do they need to make 1 or 2 constitution saving throws to maintain concentration?

A druid is concentrating on a spell, and Wild Shapes. When they take enough damage to revert, assuming there is remaining damage, do they need to make 1 or 2 constitution saving throws to maintain concentration? One.

— Jeremy Crawford (@JeremyECrawford) June 22, 2020