Whittaker only touched the ball a total of 12 times last season (five carries, seven receptions). The previous season he played a more active role, especially in the passing game, catching 25 passes (most by a Panthers RB).
The Panthers recently signed C.J. Anderson, and still have Christian McCaffrey and Cameron Artis-Payne, so they are covered at the position. Look for Artis-Payne to see a bump in playing time, especially on third downs. Unless the team signs a more proven third-down back.