What is an animal that can seriously injure a lion without fighting?

There is no major animal predator for a lion.

Animals may occasionally gang up on lions, kill a cub if they encounter one and kill weak lions or lone lionesses. But the major problem for lions is us humans. We humans have been killing animals, especially cats and particularly lions at an excessive rate. So while there are no single animal that are higher in the food chain than a lion, us humans are the ones killing them. But since you are asking what "animal" can seriously injure "a" lion, a single one, by it self on a one-on-one fight then a some animals like the African elephant or possibly a hippo can kill one. Just because of the sheer size and power of those animals.