Breathe easy, Cleveland.
Richardson is a candidate to lead the NFL in rushing attempts. The Browns will center their offense around him, and if he's lost for any significant amount of time, the drop-off will be steep. Montario Hardesty hasn't proven he can stay healthy, while Chris Ogbonnaya and Brandon Jackson are specialists and nothing more.
There's no reason to push Richardson into preseason action. He'll get his carries soon enough.