There is a world somewhere between reality and fiction. Although ignored by many, it is very real and so are those living in it. This forum is about the natural world. Here, wild animals will be heard and respected. The forum offers a glimpse into an unknown world as well as a room with a view on the present and the future. Anyone able to speak on behalf of those living in the emerald forest and the deep blue sea is invited to join.
But no, a lion is a hunter, primarily. So he needs to be able to do it.
In any case, and it would be an extreme case, the heaviest for a healthy animal would be something around 250-270 kgs, based on the single example we have.
More than that would be a fat lion and, frankly, I don't think the demands a dominant lion faces in the wild would allow him to get to that size.
Remember that lions don't just lie around all day waiting for meals as we were taught in the TV, but that they patrol their territories and they hunt.