Skip a method execution to unit test controller flow

public class DemoController : Controller
{


    private readonly ICommonOperationsRepository _commonRepo;

    public DemoController (ICommonOperationsRepository commonRepo)
    {
       _commonRepo = commonRepo;
    }
    public ActionResult Default()
    {
       var model = new DemoModel();
       try
       {
           **ConcreteClass cc = new ConcreteClass(Request.ServerVariables["HTTP_X_REWRITE_URL"].ToString());
            cc.ConcreteClassMethod();**

           model.ListTopListing.AddRange(_commonRepo.GetListings());
        }
        catch (Exception ex)
        {
            ExceptionHandler objErr = new ExceptionHandler(ex, "DemoController .Default()\n Exception : " + ex.Message);
            objErr.LogException();
         }
         return View(model);
     }

}

I am trying to unit test my controller. ConcreteClass constructor and its method ConcreteClassMethod both have some dependency on HttpRequest variables which i am not able to pass from my unit tests.

I want a way by which i can simply skip execution of ConcreteClass's constructor and ConcreteClassMethod when I am calling Default action of DemoController.