A future employer wants to talk to my past superviser who slanders me what do I do?

I have a really good chance at this job that I have been looking for but I think one of my past supervisers has been slandering me. I always give the HR number but he insists on talking to supervisers. I think this superviser is slandering me but don't want to bring it up and sound bad. What do I do if she does slander and I loose the opportunity.