Poorly frog?

Last night I was standing on the back step trying to see what was causing a commotion in the trees at the back, it was dark & the trees were shaking & I could here fluttering, think it must have been an owl or more likely the woodpigeons fidgeting! I happened to look down & there was a little frog sitting in one of the pots by the door but it looked very thin with it's bones sticking up at a sharp angle in it's back. It looked like a young adult but with a large head & small body & I was wondering if it looks too thin to everyone else or is it maybe just not fully grown/developed? It shouldn't be short of food, the garden is full of slugs & snails!