diff --git a/CHANGELOG.md b/CHANGELOG.md
index f75078251670a..dccee7b6c6402 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,4 +16,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ### Security
 
+### Changed
+
+- Change single shard assignment log message from warn to debug ([#18186](https://github.com/opensearch-project/OpenSearch/pull/18186))
+
 [Unreleased 2.19.x]: https://github.com/opensearch-project/OpenSearch/compare/fd9a9d90df25bea1af2c6a85039692e815b894f5...2.19
diff --git a/server/src/main/java/org/opensearch/cluster/routing/allocation/AllocationService.java b/server/src/main/java/org/opensearch/cluster/routing/allocation/AllocationService.java
index 78f17c9ff212b..6487f5fd70aea 100644
--- a/server/src/main/java/org/opensearch/cluster/routing/allocation/AllocationService.java
+++ b/server/src/main/java/org/opensearch/cluster/routing/allocation/AllocationService.java
@@ -598,7 +598,7 @@ private void allocateExistingUnassignedShards(RoutingAllocation allocation) {
             allocateAllUnassignedShards(allocation);
             return;
         }
-        logger.warn("Falling back to single shard assignment since batch mode disable or multiple custom allocators set");
+        logger.debug("Falling back to single shard assignment since batch mode disable or multiple custom allocators set");
 
         final RoutingNodes.UnassignedShards.UnassignedIterator primaryIterator = allocation.routingNodes().unassigned().iterator();
         while (primaryIterator.hasNext()) {