If we want to use Telerik ASP.NET AJAX controls in MVC project, we must also use either ScriptManager or RadScriptManager. But since neither works very well here is more MVC friendly solution:

 public class RadMvcScriptManager : RadScriptManager
    {
        static string JavaScriptBlockFormat = @"<script type=""text/javascript"">
//<![CDATA[ 
    {0}
//]]>
</script>";

        protected override void Render(HtmlTextWriter writer)
        {
            foreach (RegisteredScript script in GetRegisteredClientScriptBlocks())
            {
                if (HttpContext.Current.Items[script.Key] == null)
                {
                    HttpContext.Current.Items[script.Key] = true;

                    if (script.ScriptType == RegisteredScriptType.ClientScriptInclude)
                    {
                        writer.WriteLine(String.Format(@"<script type=""text/javascript"" src=""{0}""></script>", 
                            HttpUtility.HtmlEncode(script.Url)));
                    }
                }
            }



            if (HttpContext.Current.Items["AppInitialize"] == null)
            {
                Page.Items["AppInitialize"] = true;
                writer.WriteLine(
                    String.Format(
                    JavaScriptBlockFormat, 
                    @"if(typeof(Sys) != ""undefined""){
                        $addHandler(window, ""load"", function(){Sys.Application.initialize();}); } 
                    else { throw new Error(""Microsoft ASP.NET AJAX cannot be initialized!"")}"));
            }

            StringBuilder builder = new StringBuilder();

            if (HasReflectionPermission())
            {
                SerializeScriptsForScriptControls(Page, builder);
            }

            string scriptContent = builder.ToString();
            if (!String.IsNullOrEmpty(scriptContent))
            {
                writer.WriteLine(String.Format(
                       JavaScriptBlockFormat, 
                       String.Format("Sys.Application.add_init(function(){{{0}}});", scriptContent)));
            }
        }

        internal void SerializeScriptsForScriptControls(Control control, StringBuilder builder)
        {
            if (control is IScriptControl && control.Visible)
            {
                IEnumerable<ScriptDescriptor> descriptors = ((IScriptControl)control).GetScriptDescriptors();
                if (descriptors != null)
                {
                    foreach (ScriptDescriptor descriptor in descriptors)
                    {
                        SerializeScriptControlDescriptor(descriptor, builder);
                    }
                }
            }

            if (control.HasControls())
            {
                foreach (Control child in control.Controls)
                {
                    SerializeScriptsForScriptControls(child, builder);
                }
            }
        }

        internal void SerializeScriptControlDescriptor(ScriptDescriptor descriptor, StringBuilder builder)
        {
            MethodInfo getScriptInfo = descriptor.GetType().GetMethod(
                "GetScript", 
                BindingFlags.Instance | BindingFlags.NonPublic);
            if (getScriptInfo != null)
            {
                string script = (string)getScriptInfo.Invoke(descriptor, new object[] { });
                builder.AppendLine(script);
            }
        }

        internal static bool HasReflectionPermission()
        {
            try
            {
                new ReflectionPermission(ReflectionPermissionFlag.MemberAccess).Demand();
                return true;
            }
            catch (SecurityException)
            {
                return false;
            }
        }
    }