diff --git a/packages/core/src/defer/dom_triggers.ts b/packages/core/src/defer/dom_triggers.ts
index 4f75bc2bc0f0..d30eaad28fd1 100644
--- a/packages/core/src/defer/dom_triggers.ts
+++ b/packages/core/src/defer/dom_triggers.ts
@@ -31,6 +31,7 @@ import {
   TriggerType,
 } from './interfaces';
 import {getLDeferBlockDetails} from './utils';
+import {shouldTriggerDeferBlock} from './rendering';
 
 /**
  * Wrapper for onViewport trigger with angular specific Injector for resolving NgZone instance
@@ -134,6 +135,10 @@ export function registerDomTrigger<O>(
   type: TriggerType,
   options?: O,
 ) {
+  if (!shouldTriggerDeferBlock(type, initialLView)) {
+    return;
+  }
+
   const injector = initialLView[INJECTOR];
   const zone = injector.get(NgZone);
   let poll: AfterRenderRef;
diff --git a/packages/core/src/defer/rendering.ts b/packages/core/src/defer/rendering.ts
index 9fe262dada72..e5fab5dcf57e 100644
--- a/packages/core/src/defer/rendering.ts
+++ b/packages/core/src/defer/rendering.ts
@@ -7,7 +7,6 @@
  */
 
 import {CachedInjectorService} from '../cached_injector_service';
-import {NotificationSource} from '../change_detection/scheduling/zoneless_scheduling';
 import {EnvironmentInjector, InjectionToken, Injector, Provider} from '../di';
 import {
   DehydratedContainerView,
@@ -26,6 +25,7 @@ import {assertDefined} from '../util/assert';
 
 import {
   DEFER_BLOCK_STATE,
+  DeferBlockBehavior,
   DeferBlockConfig,
   DeferBlockDependencyInterceptor,
   DeferBlockInternalState,
@@ -40,6 +40,7 @@ import {
   SSR_BLOCK_STATE,
   STATE_IS_FROZEN_UNTIL,
   TDeferBlockDetails,
+  TriggerType,
 } from './interfaces';
 import {scheduleTimerTrigger} from './timer_scheduler';
 import {
@@ -485,3 +486,21 @@ export function ɵɵdeferEnableTimerScheduling(
     applyDeferBlockStateWithSchedulingImpl = applyDeferBlockStateWithScheduling;
   }
 }
+
+/**
+ * Determines whether we should proceed with triggering a given defer block.
+ */
+export function shouldTriggerDeferBlock(triggerType: TriggerType, lView: LView): boolean {
+  // prevents triggering regular triggers when on the server.
+  if (triggerType === TriggerType.Regular && typeof ngServerMode !== 'undefined' && ngServerMode) {
+    return false;
+  }
+
+  // prevents triggering in the case of a test run with manual defer block configuration.
+  const injector = lView[INJECTOR];
+  const config = injector.get(DEFER_BLOCK_CONFIG, null, {optional: true});
+  if (config?.behavior === DeferBlockBehavior.Manual) {
+    return false;
+  }
+  return true;
+}
diff --git a/packages/core/src/defer/triggering.ts b/packages/core/src/defer/triggering.ts
index a1b865dea51b..cd69a12e73e9 100644
--- a/packages/core/src/defer/triggering.ts
+++ b/packages/core/src/defer/triggering.ts
@@ -41,7 +41,6 @@ import {onViewportWrapper} from './dom_triggers';
 import {onIdle} from './idle_scheduler';
 import {
   DEFER_BLOCK_STATE,
-  DeferBlockBehavior,
   DeferBlockState,
   DeferBlockTrigger,
   DeferDependenciesLoadingState,
@@ -56,11 +55,11 @@ import {
 } from './interfaces';
 import {DEHYDRATED_BLOCK_REGISTRY, DehydratedBlockRegistry} from './registry';
 import {
-  DEFER_BLOCK_CONFIG,
   DEFER_BLOCK_DEPENDENCY_INTERCEPTOR,
   renderDeferBlockState,
   renderDeferStateAfterResourceLoading,
   renderPlaceholder,
+  shouldTriggerDeferBlock,
 } from './rendering';
 import {onTimer} from './timer_scheduler';
 import {
@@ -313,24 +312,6 @@ export function triggerResourceLoading(
   });
 }
 
-/**
- * Defines whether we should proceed with triggering a given defer block.
- */
-function shouldTriggerDeferBlock(triggerType: TriggerType, lView: LView): boolean {
-  // prevents triggering regular triggers when on the server.
-  if (triggerType === TriggerType.Regular && typeof ngServerMode !== 'undefined' && ngServerMode) {
-    return false;
-  }
-
-  // prevents triggering in the case of a test run with manual defer block configuration.
-  const injector = lView[INJECTOR];
-  const config = injector.get(DEFER_BLOCK_CONFIG, null, {optional: true});
-  if (config?.behavior === DeferBlockBehavior.Manual) {
-    return false;
-  }
-  return true;
-}
-
 /**
  * Attempts to trigger loading of defer block dependencies.
  * If the block is already in a loading, completed or an error state -
diff --git a/packages/core/test/acceptance/defer_spec.ts b/packages/core/test/acceptance/defer_spec.ts
index 75f452160039..dbce77f13761 100644
--- a/packages/core/test/acceptance/defer_spec.ts
+++ b/packages/core/test/acceptance/defer_spec.ts
@@ -48,7 +48,15 @@ import {ChainedInjector} from '../../src/render3/chained_injector';
 import {getComponentDef} from '../../src/render3/def_getters';
 import {getInjectorResolutionPath} from '../../src/render3/util/injector_discovery_utils';
 import {global} from '../../src/util/global';
-import {ComponentFixture, DeferBlockBehavior, fakeAsync, flush, TestBed, tick} from '../../testing';
+import {
+  ComponentFixture,
+  DeferBlockBehavior,
+  DeferBlockState,
+  fakeAsync,
+  flush,
+  TestBed,
+  tick,
+} from '../../testing';
 
 /**
  * Clears all associated directive defs from a given component class.
@@ -4532,7 +4540,6 @@ describe('@defer', () => {
                 @placeholder {<button>p{{item}} </button>}
               }
            `,
-      
         changeDetection: ChangeDetectionStrategy.Eager,})
       class MyCmp {
         items = [1, 2, 3, 4, 5, 6];
@@ -4652,6 +4659,36 @@ describe('@defer', () => {
       expect(activeObservers[2].observedElements.has(button)).toBe(true);
       expect(activeObservers[2].options).toEqual({rootMargin: '1vh'});
     }));
+
+    it('should not attach observer if rendering manually', async () => {
+      @Component({
+        template: `
+          @defer (on viewport(trigger)) {
+            Main content
+          } @placeholder {
+            Placeholder
+          }
+
+          <button #trigger></button>
+        `,
+      })
+      class MyCmp {}
+
+      TestBed.configureTestingModule({
+        deferBlockBehavior: DeferBlockBehavior.Manual,
+      });
+      const fixture = TestBed.createComponent(MyCmp);
+      fixture.detectChanges();
+
+      expect(activeObservers.length).toBe(0);
+      expect(fixture.nativeElement.textContent.trim()).toBe('Placeholder');
+
+      const deferBlock = (await fixture.getDeferBlocks())[0];
+      await deferBlock.render(DeferBlockState.Complete);
+
+      expect(activeObservers.length).toBe(0);
+      expect(fixture.nativeElement.textContent.trim()).toBe('Main content');
+    });
   });
 
   describe('DOM-based events cleanup', () => {