There is not a lot to say on this topic because the lion is the top predator in Africa bar one: the human. Therefore technically or theoretically no animal kills the lion to eat it as a meal.
However, the question is open to any interpretation. The human does kill the lion and the human also eats the lion in the form of lion steaks. Admittedly not many people indulge in this bizarre eating habit but there are some who like to do it. See also lion burger special. Most lion meat is home reared, believe it or not, somewhat like livestock.
Therefore when people ask, “what eats a lion?”, the best answer is The Human. That is not the complete answer. There are other circumstances which leaves the mighty lion vulnerable.
Following a pride takeover, incoming male lions kill small cubs thereby inducing females to come into oestrus and mate. However, the male lions don’t eat the cubs (as I understand it) but it is worth mentioning. This is lion infanticide.
Alone, lion cubs are defenceless. Many are killed by leopards and hyenas and other lions. I presume the leopards and hyenas eat the cubs. I am not sure if the lions do. They probably do.
Old and infirm lions and lionesses may be successfully attacked and eaten by leopards and hyenas. I have not heard of a gang of hyenas attacking a healthy lion to kill for food. The hyena is deferential towards the lion although as a gang they do sometimes push lions and lionesses off their kill to steal it. Vice versa also happens.
Canned lion hunting is popular in South Africa. Are the killed lions shipped to countries where they are eaten by people? Tiger meat is popular in China. Do the Chinese in China also eat lion? I expect so.
Gerard Depardieu says he shot and ate lions in Africa! True or false? Not sure.