How to Backbone Validation based from HTTP Response?

I am currently creating a Form using Backbone.js. I am completely new to Backbone.js. I have the frontend validation but I need to validate a specific field after focus out or a validate button click.

I have the logic on Model:

company: [
       function (value, name) {
                 return Validator.required(value, Utils.translate('Company is required'));
       },
       function (value, name) { 
                 //Backend validation here
       }
]

Can I tried to insert an AJAX request but it won’t work due to delay.

Any recommendations on how can I achieve this?