Pierre Thomas worth adding?

We use a salary cap in my league and its always good to have some cap space, i was thinking of dropping selvin young for pierre thomas who is about half as much. As it is now i dont even need to start Young i just have him in case he becomes the feature back, I think he could be a great fantasy if that happens, but it doesnt look like it will. It seems more likely that Thomas will be taking over McCallisters old role. I may play wait and see but since I am currently in first place id get last shot if thomas has a big week next week. I didnt see the saints game so I don't know if he looked good or TB's D looked bad. Any advice?