diff --git a/modules/userId/index.js b/modules/userId/index.js
index d0299427603..2a9d1f27072 100644
--- a/modules/userId/index.js
+++ b/modules/userId/index.js
@@ -165,9 +165,6 @@ export const dep = {
   isAllowed: isActivityAllowed
 }
 
-/** @type {boolean} */
-let addedUserIdHook = false;
-
 /** @type {SubmoduleContainer[]} */
 let submodules = [];
 
@@ -693,6 +690,25 @@ export const startAuctionHook = timedAuctionHook('userId', function requestBidsH
   });
 });
 
+/**
+ * Append user id data from config to bids to be accessed in adapters when there are no submodules.
+ * @param {function} fn required; The next function in the chain, used by hook.js
+ * @param {Object} reqBidsConfigObj required; This is the same param that's used in pbjs.requestBids.
+ */
+export const addUserIdsHook = timedAuctionHook('userId', function requestBidsHook(fn, reqBidsConfigObj) {
+  addIdData(reqBidsConfigObj);
+  // calling fn allows prebid to continue processing
+  fn.call(this, reqBidsConfigObj);
+});
+
+/**
+ * Is startAuctionHook added
+ * @returns {boolean}
+ */
+function addedStartAuctionHook() {
+  return !!startAuction.getHooks({hook: startAuctionHook}).length;
+}
+
 /**
  * This function will be exposed in global-name-space so that userIds stored by Prebid UserId module can be used by external codes as well.
  * Simple use case will be passing these UserIds to A9 wrapper solution
@@ -1110,11 +1126,11 @@ function updateSubmodules() {
     .forEach((sm) => submodules.push(sm));
 
   if (submodules.length) {
-    if (!addedUserIdHook) {
+    if (!addedStartAuctionHook()) {
+      startAuction.getHooks({hook: addUserIdsHook}).remove();
       startAuction.before(startAuctionHook, 100) // use higher priority than dataController / rtd
       adapterManager.callDataDeletionRequest.before(requestDataDeletion);
       coreGetPPID.after((next) => next(getPPID()));
-      addedUserIdHook = true;
     }
     logInfo(`${MODULE_NAME} - usersync config updated for ${submodules.length} submodules: `, submodules.map(a => a.submodule.name));
   }
@@ -1221,6 +1237,10 @@ export function init(config, {delay = GreedyPromise.timeout} = {}) {
   (getGlobal()).refreshUserIds = normalizePromise(refreshUserIds);
   (getGlobal()).getUserIdsAsync = normalizePromise(getUserIdsAsync);
   (getGlobal()).getUserIdsAsEidBySource = getUserIdsAsEidBySource;
+  if (!addedStartAuctionHook()) {
+    // Add ortb2.user.ext.eids even if 0 submodules are added
+    startAuction.before(addUserIdsHook, 100); // use higher priority than dataController / rtd
+  }
 }
 
 // init config update listener to start the application
diff --git a/test/spec/modules/userId_spec.js b/test/spec/modules/userId_spec.js
index 6ebe533e260..c4f333e56ac 100644
--- a/test/spec/modules/userId_spec.js
+++ b/test/spec/modules/userId_spec.js
@@ -8,6 +8,7 @@ import {
   init,
   PBJS_USER_ID_OPTOUT_NAME,
   startAuctionHook,
+  addUserIdsHook,
   requestDataDeletion,
   setStoredValue,
   setSubmoduleRegistry,
@@ -27,6 +28,7 @@ import {sharedIdSystemSubmodule} from 'modules/sharedIdSystem.js';
 import {pubProvidedIdSubmodule} from 'modules/pubProvidedIdSystem.js';
 import * as mockGpt from '../integration/faker/googletag.js';
 import 'src/prebid.js';
+import {startAuction} from 'src/prebid';
 import {hook} from '../../../src/hook.js';
 import {mockGdprConsent} from '../../helpers/consentData.js';
 import {getPPID} from '../../../src/adserver.js';
@@ -175,6 +177,8 @@ describe('User ID', function () {
   afterEach(() => {
     sandbox.restore();
     config.resetConfig();
+    startAuction.getHooks({hook: startAuctionHook}).remove();
+    startAuction.getHooks({hook: addUserIdsHook}).remove();
   });
 
   after(() => {
@@ -2423,6 +2427,58 @@ describe('User ID', function () {
         })
       })
     });
+
+    describe('submodules not added', () => {
+      const eid = {
+        source: 'example.com',
+        uids: [{id: '1234', atype: 3}]
+      };
+      let adUnits;
+      let startAuctionStub;
+      function saHook(fn, ...args) {
+        return startAuctionStub(...args);
+      }
+      beforeEach(() => {
+        adUnits = [{code: 'au1', bids: [{bidder: 'sampleBidder'}]}];
+        startAuctionStub = sinon.stub();
+        startAuction.before(saHook);
+        config.resetConfig();
+      });
+      afterEach(() => {
+        startAuction.getHooks({hook: saHook}).remove();
+      })
+
+      it('addUserIdsHook', function (done) {
+        addUserIdsHook(function () {
+          adUnits.forEach(unit => {
+            unit.bids.forEach(bid => {
+              expect(bid).to.have.deep.nested.property('userIdAsEids.0.source');
+              expect(bid).to.have.deep.nested.property('userIdAsEids.0.uids.0.id');
+              expect(bid.userIdAsEids[0].source).to.equal('example.com');
+              expect(bid.userIdAsEids[0].uids[0].id).to.equal('1234');
+            });
+          });
+          done();
+        }, {
+          adUnits,
+          ortb2Fragments: {
+            global: {user: {ext: {eids: [eid]}}},
+            bidder: {}
+          }
+        });
+      });
+
+      it('should add userIdAsEids and merge ortb2.user.ext.eids even if no User ID submodules', () => {
+        init(config);
+        config.setConfig({
+          ortb2: {user: {ext: {eids: [eid]}}}
+        })
+        expect(startAuction.getHooks({hook: startAuctionHook}).length).equal(0);
+        expect(startAuction.getHooks({hook: addUserIdsHook}).length).equal(1);
+        $$PREBID_GLOBAL$$.requestBids({adUnits});
+        sinon.assert.calledWith(startAuctionStub, sinon.match.hasNested('adUnits[0].bids[0].userIdAsEids[0]', eid));
+      });
+    });
   });
 
   describe('handles config with ESP configuration in user sync object', function() {