Go to My Madden then go to Creation Zone then when you see Create-A-Player press A.  Create a ROOKIE (or the cheat doesn't work)with his attributes(player rating) maxed out. So you create a player however you want, just keep his "years pro" to 0 and max out his attributes. Save your player. Go to career modes press A at Be an NFL Superstar mode, the choose a rookie then choose your created player.