diff --git a/src/GraphQL.Client/GraphQLHttpRequest.cs b/src/GraphQL.Client/GraphQLHttpRequest.cs
index 9ff0c600..c9d4e01a 100644
--- a/src/GraphQL.Client/GraphQLHttpRequest.cs
+++ b/src/GraphQL.Client/GraphQLHttpRequest.cs
@@ -1,5 +1,4 @@
 using System.Net.Http.Headers;
-using System.Runtime.Serialization;
 using System.Text;
 using GraphQL.Client.Abstractions;
 
@@ -21,13 +20,6 @@ public GraphQLHttpRequest(GraphQLRequest other)
     {
     }
 
-    /// <summary>
-    /// Allows to preprocess a <see cref="HttpRequestMessage"/> before it is sent, i.e. add custom headers
-    /// </summary>
-    [IgnoreDataMember]
-    [Obsolete("Inherit from GraphQLHttpRequest and override ToHttpRequestMessage() to customize the HttpRequestMessage. Will be removed in v4.0.0.")]
-    public Action<HttpRequestMessage> PreprocessHttpRequestMessage { get; set; } = message => { };
-
     /// <summary>
     /// Creates a <see cref="HttpRequestMessage"/> from this <see cref="GraphQLHttpRequest"/>.
     /// Used by <see cref="GraphQLHttpClient"/> to convert GraphQL requests when sending them as regular HTTP requests.
@@ -48,9 +40,6 @@ public virtual HttpRequestMessage ToHttpRequestMessage(GraphQLHttpClientOptions
         if (options.DefaultUserAgentRequestHeader != null)
             message.Headers.UserAgent.Add(options.DefaultUserAgentRequestHeader);
 
-#pragma warning disable CS0618 // Type or member is obsolete
-        PreprocessHttpRequestMessage(message);
-#pragma warning restore CS0618 // Type or member is obsolete
         return message;
     }
 }
diff --git a/tests/GraphQL.Integration.Tests/QueryAndMutationTests/Base.cs b/tests/GraphQL.Integration.Tests/QueryAndMutationTests/Base.cs
index bff54832..0b120ba4 100644
--- a/tests/GraphQL.Integration.Tests/QueryAndMutationTests/Base.cs
+++ b/tests/GraphQL.Integration.Tests/QueryAndMutationTests/Base.cs
@@ -163,28 +163,6 @@ query Human($id: String!){
         Assert.Equal("Han Solo", queryResponse.Data.Human.Name);
     }
 
-    [Fact]
-    public async void PreprocessHttpRequestMessageIsCalled()
-    {
-        var callbackTester = new CallbackMonitor<HttpRequestMessage>();
-        var graphQLRequest = new GraphQLHttpRequest($"{{ human(id: \"1\") {{ name }} }}")
-        {
-#pragma warning disable CS0618 // Type or member is obsolete
-            PreprocessHttpRequestMessage = callbackTester.Invoke
-#pragma warning restore CS0618 // Type or member is obsolete
-        };
-
-        var expectedHeaders = new HttpRequestMessage().Headers;
-        expectedHeaders.UserAgent.Add(new ProductInfoHeaderValue("GraphQL.Client", typeof(GraphQLHttpClient).Assembly.GetName().Version.ToString()));
-        expectedHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/graphql-response+json"));
-        expectedHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
-        expectedHeaders.AcceptCharset.Add(new StringWithQualityHeaderValue("utf-8"));
-        var response = await StarWarsClient.SendQueryAsync(graphQLRequest, () => new { Human = new { Name = string.Empty } });
-        callbackTester.Should().HaveBeenInvokedWithPayload().Which.Headers.Should().BeEquivalentTo(expectedHeaders);
-        Assert.Null(response.Errors);
-        Assert.Equal("Luke", response.Data.Human.Name);
-    }
-
     [Fact]
     public async Task PostRequestCanBeCancelled()
     {