Hello, I am not a complete beginner, but I am not skilled enough to model a Lion. I have found other tutorials on modeling quadrepeds but they haven't helped much. Can somebody please point me in the right direction?

Did you find a cat-specific one? A lion is pretty similar to other cats, except for the face and mane, and the tail tuft. If you can't find a cat blueprint then find some good lion photos and make yourself one; making blueprints from photos is pretty easy.

If you have the time and want to go phtotrealistic, also search for anatomic images (muscle, bones, fatty layers, and so on) of cats. But be aware that there is a limit to what you can find on the net, maybe also look for good books.

I bought a very old book (correction: new edition of a very old book) on animal anatomy for artists, which shows the anatomy in detail. I only used it once, but it seems detailled enough for these crazy sculpting sessions where you try to get every muscle right (and curse your inability to do so).

This is the book I got: http://www.amazon.com/Atlas-Animal-Anatomy-Artists-Dover/dp/0486200825/ref=sr_1_2?ie=UTF8&qid=1407232212&sr=8-2&keywords=animal+anatomy