This is a really good photo. I like the slight brown toning because it gives the shadows a more inky, rich look. There is also a good depth of field effect, with the blurred background and foreground. The darker area at the top of the frame helps to separate the rabbit from the grass, so it stands out better.

In this photo selective sharpening could work really well too, by carefully painting in small radius, fine sharpening in areas like the eye and the fur, and no sharpening or even a slight blur in the grass.

One easy way to select the grass that may work would be to use the Select > Color Range command. Click the grass with the eyedropper in the Color Range dialog to sample the color. With the fuzziness slider you can expand or contract the selection. Sometimes this works very well for me.

I like this result... after all the rabbits are supposed to be able to hide with their mimetic mantle in a meadow. However, a technique you could have use in this case was to take advantage of the different color of the rabbit with the grass. I imagine the grass was prevalently green and the rabbit grey-brown. With the channel mixer, turning to negative the green channel, and boosting the red and blue would have probably created a dark background with a lighter rabbit.

Thanks for your helpful comments Alex and Massimo. I've been away so I haven't had time to work on this photo, but I will try out the things you suggested and let you know if I can improve this one!