How to file a case for defamation and ruining business reputation?

Is there any legal action I can take against a person for spreading false hearsay stories publicly which are false and not even linked to his company & he never checks with me on the true facts?

The background story: I have legal negotiations and proceedings going on with a company that signed a business deal (between companies) with my company registered outside the UAE.

While all this is ongoing legally, I get to know that the employee of this company with whom I am legally negotiating the disputed contract separately has gone and spoken to my ex-employer's CEO (as they are good friends) and they have started telling rumors and wrong facts in the market making everyone think that "I ran away with the money".

This is ruining my reputation with friends and ex-colleagues with whom I worked for a decade and also in the industry I worked in generally in Dubai.

I do have at least 3 people who have come forward and told me about these stories from the same ex-employer.

Appreciate guidance.