diff --git a/core/metacling/src/TClingCallbacks.cxx b/core/metacling/src/TClingCallbacks.cxx
index d8ce47ba40196..2be13f2865373 100644
--- a/core/metacling/src/TClingCallbacks.cxx
+++ b/core/metacling/src/TClingCallbacks.cxx
@@ -33,6 +33,7 @@
 #include "clang/Sema/Scope.h"
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/GlobalModuleIndex.h"
+#include "clang/Basic/DiagnosticSema.h"
 
 #include "llvm/ExecutionEngine/Orc/Core.h"
 
@@ -1004,6 +1005,12 @@ bool TClingCallbacks::tryInjectImplicitAutoKeyword(LookupResult &R, Scope *S) {
    Result->addAttr(AnnotateAttr::CreateImplicit(C, "__Auto"));
 
    R.addDecl(Result);
+
+   // Raise a warning when trying to use implicit auto injection feature.
+   SemaRef.getDiagnostics().setSeverity(diag::warn_deprecated_message, diag::Severity::Warning, SourceLocation());
+   SemaRef.Diag(Loc, diag::warn_deprecated_message)
+      << "declaration without the 'auto' keyword" << DC << Loc << FixItHint::CreateInsertion(Loc, "auto ");
+
    // Say that we can handle the situation. Clang should try to recover
    return true;
 }
diff --git a/core/metacling/test/TClingTests.cxx b/core/metacling/test/TClingTests.cxx
index 329938de9ea49..b94656864f66c 100644
--- a/core/metacling/test/TClingTests.cxx
+++ b/core/metacling/test/TClingTests.cxx
@@ -239,6 +239,19 @@ TEST_F(TClingTests, GetSharedLibDeps)
 }
 #endif
 
+// Check that a warning message is generated when using auto-injection.
+TEST_F(TClingTests, WarningAutoInjection)
+{
+   ROOT::TestSupport::CheckDiagsRAII diags;
+   diags.requiredDiag(kWarning, "cling", "declaration without the 'auto' keyword is deprecated",
+                      /*matchFullMessage=*/false);
+
+   gInterpreter->ProcessLine("/* no auto */ t = new int;");
+
+   auto t = gInterpreter->GetDataMember(nullptr, "t");
+   EXPECT_TRUE(t != nullptr);
+}
+
 // Check the interface which interacts with the cling::LookupHelper.
 TEST_F(TClingTests, ClingLookupHelper) {
   // Exception spec evaluation.