Previous Co-worker spread false comments about me to a prospective employer, ruined my reputation

I recently applied at a company and coincidentally knew an individual that worked there, who gave me an initial recommendation. However an individual at my PREVIOUS employer knew the hiring manager there and stated false, incorrect statements about my character, which caused me to not even get an interview opportunity. My source informed me that because of that feedback, which was completely false, that I probably won't even get an interview now. So in essence, an individual at a PREVIOUS employer of mine not only jeopardized my possibility at an interview, but most importantly, tarnished my reputation as well. What steps should I take to handle this matter legally? Would I be suing the individual or the company (where I used to work as well in the past) which he works for currently?