Rcpp Class wrapped in S4 object warning

I have an R package that utilises an Rcpp Module that contains an Rcpp class that is exposed to the R namespace. The package builds OK and runs fine.

Here is the S4 object definition:

#' The main class object
#' @export
setClass("MyObject",
       representation(
            index = "Rcpp_ModuleClass",
            field = "character",
            other_field = "raw")) 

I keep getting this warning that I found no solution how to get rid of

Warning: undefined slot classes in definition of "MyObject": index(class "Rcpp_ModuleClass")

Is there a way that I can load an Rcpp module and point the class definition to the definition of the S4 object?