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If there is a warrant out for your arrest the police may have notified the airports to watch out for you, but the only way you will find out is if you either hand yourself into police or turn up at the airport ready to travel. The reality is that the police do not tell people there is a warrant out for their arrest in advance, they simply obtain a warrant from the court and then arrest people.
If you elaborate on the circumstances which have given rise to the alleged assault or can explain why this person has said you may have a warrant out for assault I may be able to comment further, otherwise please rate my answer.
The police may just be looking for you to interview you, though if a CAN has been issued to you and you failed to appear in court then it is certainly possible that an arrest warrant has been issued by the court. Whether they have also taken steps to prevent you obtaining a passport or leaving the country will be uncertain given the circumstances you describe would tend to suggest the offence is a relatively minor one.
You could just present yourself to the police station and explain that you never received the CAN, but if an arrest warrant has been issued, that may result in your being held until the matter can be brought before the court, so if you want to minimise the chances of that I would recommend you see a lawyer in advance of handing yourself in, and in any event if you have been charged, you should engage a lawyer to assist you.
I appreciate this is not the clear cut answer you likely were hoping for but it does reflect the legal reality of your situation.
Good luck and please rate my answer.