If it's just a still, I'd do it in Photoshop or After Effects with the clone stamp tool. There's plenty of clean grass to use to paint over the player's real position.
Sorry I should've been clearer. I want to animate his movement path so it has him moving across the image.
You don't need any content aware other than creating a big static image layer you put under the "holes" you are going to create by cutting out the player and moving it around. For still images this is best doen in photoshop. No need to make it more complicated than that, give or take a few specific issues with the lines and shadows. Trying to do this in AE would have the disadvantage of causing additional jitter/ flicker, anyway. You simply have a wrong idea about the workflow.
Thanks for your replies all. Can you give me a name for the process or direct me toward a tutorial?
It's fairly straightforward. If you need to, export a still frame of the image from AE, or otherwise use the original source.
Open in Photoshop and make two duplicate layers of the whole image. It's not essential, but personally I always retain the background layer as the original contnent, so there's always a backup if you need it.
On the upper layer, erase everything except the player. Use whatever tools you prefer - masks, eraser, the selector tools, whatever you like.
On the lower image, use the Clone Stamp tool to clone areas of plain grass over the player, effectively painting him out. With some careful cloning you should be able to rebuild the white field marking below him.
Save the document and import to After Effects as a Composition. You'll now have a clean background layer and an isolated player that you can animate over the top.