Perhaps, or perhaps this clone just isn't as strong as the rest of them. A lot of times, when I find a clone that wilts more than the rest, I just go ahead and cull it to make room for the vibrant, more healthy ones. Try not to let the topsoil dry out for the next few days, just to ensure that the roots are able to get water. Hopefully it'll pull through on it's own volition.

Also, are you feeding it with a nutrient solution, or just plain water?