diff --git a/tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/ConfigureIntegration.cs b/tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/ConfigureIntegration.cs
index cd5c0c751dc9..c58650f96475 100644
--- a/tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/ConfigureIntegration.cs
+++ b/tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/ManualInstrumentation/Tracer/ConfigureIntegration.cs
@@ -1,4 +1,4 @@
-// <copyright file="ConfigureIntegration.cs" company="Datadog">
+// <copyright file="ConfigureIntegration.cs" company="Datadog">
 // Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
 // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
 // </copyright>
@@ -11,6 +11,7 @@
 using Datadog.Trace.Configuration.ConfigurationSources;
 using Datadog.Trace.Configuration.ConfigurationSources.Telemetry;
 using Datadog.Trace.Configuration.Telemetry;
+using Datadog.Trace.Logging;
 using Datadog.Trace.Telemetry;
 using Datadog.Trace.Telemetry.Metrics;
 
@@ -32,6 +33,8 @@ namespace Datadog.Trace.ClrProfiler.AutoInstrumentation.ManualInstrumentation.Tr
 [EditorBrowsable(EditorBrowsableState.Never)]
 public class ConfigureIntegration
 {
+    private static readonly IDatadogLogger Log = DatadogLogging.GetLoggerFor<ConfigureIntegration>();
+
     internal static CallTargetState OnMethodBegin<TTarget>(Dictionary<string, object?> values)
     {
         ConfigureSettingsWithManualOverrides(values, useLegacySettings: false);
@@ -43,6 +46,14 @@ internal static void ConfigureSettingsWithManualOverrides(Dictionary<string, obj
     {
         TelemetryFactory.Metrics.Record(PublicApiUsage.Tracer_Configure);
 
+        // If the current tracer manager is locked (e.g., CI Test Optimization),
+        // do not attempt to replace it to avoid throwing in CreateInitializedTracer.
+        if (TracerManager.Instance is ILockedTracer)
+        {
+            Log.Information("Skipping Tracer.Configure from manual instrumentation because the current tracer instance is locked and cannot be replaced.");
+            return;
+        }
+
         // Is this from calling new TracerSettings() or TracerSettings.Global?
         var isFromDefaults = values.TryGetValue(TracerSettingKeyConstants.IsFromDefaultSourcesKey, out var value) && value is true;
 
diff --git a/tracer/test/Datadog.Trace.Tests/ManualInstrumentation/ConfigureIntegrationTests.cs b/tracer/test/Datadog.Trace.Tests/ManualInstrumentation/ConfigureIntegrationTests.cs
new file mode 100644
index 000000000000..ae572d058a31
--- /dev/null
+++ b/tracer/test/Datadog.Trace.Tests/ManualInstrumentation/ConfigureIntegrationTests.cs
@@ -0,0 +1,45 @@
+// <copyright file="ConfigureIntegrationTests.cs" company="Datadog">
+// Unless explicitly stated otherwise all files in this repository are licensed under the Apache 2 License.
+// This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
+// </copyright>
+
+#nullable enable
+
+using System.Collections.Generic;
+using Datadog.Trace.Agent;
+using Datadog.Trace.ClrProfiler.AutoInstrumentation.ManualInstrumentation.Tracer;
+using Datadog.Trace.Configuration;
+using Datadog.Trace.Logging.TracerFlare;
+using Datadog.Trace.RemoteConfigurationManagement;
+using Datadog.Trace.TestHelpers;
+using FluentAssertions;
+using Moq;
+using Xunit;
+
+namespace Datadog.Trace.Tests.ManualInstrumentation;
+
+[Collection(nameof(TracerInstanceTestCollection))]
+[TracerRestorer]
+public class ConfigureIntegrationTests
+{
+    [Fact]
+    public void ConfigureSettingsWithManualOverrides_DoesNotThrow_WhenTracerIsLocked()
+    {
+        // Arrange: lock the global tracer manager
+        TracerManager.UnsafeReplaceGlobalManager(new LockedTracerManager());
+        TracerManager.Instance.Should().BeAssignableTo<ILockedTracer>();
+
+        // Act/Assert: should not throw and should not replace the manager
+        ConfigureIntegration.ConfigureSettingsWithManualOverrides(new Dictionary<string, object?>(), useLegacySettings: false);
+
+        TracerManager.Instance.Should().BeAssignableTo<ILockedTracer>();
+    }
+
+    private class LockedTracerManager : TracerManager, ILockedTracer
+    {
+        public LockedTracerManager()
+            : base(new TracerSettings(), null, null, null, null, null, null, null, null, null, null, null, null, Mock.Of<IRemoteConfigurationManager>(), Mock.Of<IDynamicConfigurationManager>(), Mock.Of<ITracerFlareManager>(), Mock.Of<ISpanEventsManager>())
+        {
+        }
+    }
+}