diff --git a/src/common/utils/dom.test.ts b/src/common/utils/dom.test.ts
index f4ab21b..c949de3 100644
--- a/src/common/utils/dom.test.ts
+++ b/src/common/utils/dom.test.ts
@@ -1,13 +1,15 @@
+import { createElement } from '@common/test/utils'
 import {
   getElementById,
   getElementsByName,
+  observeElement,
   querySelector,
   querySelectorAll,
   querySelectorAllIn,
   querySelectorIn,
 } from '@common/utils/dom'
 import { logger } from '@common/utils/logger'
-import { beforeEach, describe, expect, it } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 describe(getElementById, () => {
   beforeEach(() => {
@@ -207,3 +209,41 @@ describe(querySelectorAllIn, () => {
     expect(logger.warn).not.toHaveBeenCalled()
   })
 })
+
+describe(observeElement, () => {
+  beforeEach(() => {
+    document.body.innerHTML = `
+      <div id="container">
+        <div class="content">Initial content</div>
+      </div>
+    `
+  })
+
+  it('calls callback when element children change', async () => {
+    const container = document.getElementById('container')!
+    const callback = vi.fn<() => void>()
+
+    observeElement(container, callback)
+
+    container.appendChild(createElement('New content'))
+
+    await vi.waitFor(() => {
+      expect(callback).toHaveBeenCalledTimes(1)
+    })
+  })
+
+  it('calls callback when subtree changes', async () => {
+    const container = document.getElementById('container')!
+    const callback = vi.fn<() => void>()
+
+    observeElement(container, callback)
+
+    // Modify a nested element
+    const content = container.querySelector('.content')!
+    content.textContent = 'Modified content'
+
+    await vi.waitFor(() => {
+      expect(callback).toHaveBeenCalledTimes(1)
+    })
+  })
+})
diff --git a/src/common/utils/dom.ts b/src/common/utils/dom.ts
index 27cfc5e..a72b27c 100644
--- a/src/common/utils/dom.ts
+++ b/src/common/utils/dom.ts
@@ -117,3 +117,19 @@ export const querySelectorAllIn = <E extends Element = Element>(
 
   return elements
 }
+
+/**
+ * Observe an element for DOM changes and run a callback when mutations occur.
+ *
+ * @param element - The element to observe for changes
+ * @param callback - Function to execute when the element's children change
+ */
+export const observeElement = (element: Element, callback: () => void) => {
+  const observer = new MutationObserver(() => {
+    observer.disconnect()
+    callback()
+    observer.observe(element, { childList: true, subtree: true })
+  })
+
+  observer.observe(element, { childList: true, subtree: true })
+}
diff --git a/src/modules/week-number/index.test.ts b/src/modules/week-number/index.test.ts
index 6272b60..e54dbab 100644
--- a/src/modules/week-number/index.test.ts
+++ b/src/modules/week-number/index.test.ts
@@ -1,5 +1,15 @@
+import { isPage, pages } from '@common/utils/pages'
 import weekNumber from '@modules/week-number'
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
+
+vi.mock(import('@common/utils/pages'), async () => {
+  const originalModule = await vi.importActual('@common/utils/pages')
+
+  return {
+    ...originalModule,
+    isPage: vi.fn<typeof isPage>(),
+  }
+})
 
 describe('week-number module', () => {
   it.each([
@@ -19,6 +29,30 @@ describe('week-number module', () => {
     expect(span?.textContent).toBe(expected)
   })
 
+  it.each([
+    { desc: 'own team', page: pages.playerDetailOwnTeam },
+    { desc: 'other team', page: pages.playerDetailOtherTeam },
+  ])('observes player tabs and adds week numbers on content change', async ({ page }) => {
+    vi.mocked(isPage).mockImplementation((p) => p === page)
+
+    document.body.innerHTML = `
+        <div id="mainBody">
+          <div id="ctl00_ctl00_CPContent_CPMain_updPlayerTabs"></div>
+        </div>
+      `
+    weekNumber.run()
+
+    // Simulate content update
+    const playerTabs = document.getElementById('ctl00_ctl00_CPContent_CPMain_updPlayerTabs')!
+    playerTabs.innerHTML = '<div class="date">15.05.2025</div>'
+
+    await vi.waitFor(() => {
+      const newWeekNumber = playerTabs.querySelector<HTMLSpanElement>('span.hte-week-number')
+
+      expect(newWeekNumber?.textContent).toBe(' (W3)')
+    })
+  })
+
   it("doesn't add week number for invalid date", () => {
     document.body.innerHTML = `
       <div id="mainBody">
diff --git a/src/modules/week-number/index.ts b/src/modules/week-number/index.ts
index 88da593..bc82fe2 100644
--- a/src/modules/week-number/index.ts
+++ b/src/modules/week-number/index.ts
@@ -1,10 +1,32 @@
 import '@modules/week-number/index.css'
 
 import type { Module } from '@common/types/module'
-import { querySelectorAll } from '@common/utils/dom'
-import { pages } from '@common/utils/pages'
+import { getElementById, observeElement, querySelectorAllIn } from '@common/utils/dom'
+import { isPage, pages } from '@common/utils/pages'
 import { calcWeekNumber, parseDate } from '@modules/week-number/utils'
 
+/**
+ * Add week numbers to all date elements within the given root element.
+ *
+ * @param root - The parent element to search for date elements within
+ */
+const addWeekNumbers = (root: Element) => {
+  const elements = querySelectorAllIn(root, '.date', false)
+
+  elements.forEach((element) => {
+    const date = parseDate(element)
+    if (!date) return
+
+    const weekNumber = calcWeekNumber(date)
+
+    const span = document.createElement('span')
+    span.className = 'hte-week-number shy'
+    span.textContent = ` (W${weekNumber})`
+
+    element.appendChild(span)
+  })
+}
+
 /**
  * Display week numbers next to dates throughout Hattrick.
  */
@@ -13,20 +35,21 @@ const weekNumber: Module = {
   pages: [pages.all],
   excludePages: [pages.forum],
   run: () => {
-    const elements = querySelectorAll('#mainBody .date', false)
-
-    elements.forEach((element) => {
-      const date = parseDate(element)
-      if (!date) return
+    const mainBody = getElementById('mainBody')
+    if (!mainBody) return
 
-      const weekNumber = calcWeekNumber(date)
+    addWeekNumbers(mainBody)
 
-      const span = document.createElement('span')
-      span.className = 'hte-week-number shy'
-      span.textContent = ` (W${weekNumber})`
+    // Watch for tab changes on the player detail page. Tab content is loaded asynchronously when clicked, so we need to
+    // re-apply week numbers after each update.
+    if (isPage(pages.playerDetailOwnTeam) || isPage(pages.playerDetailOtherTeam)) {
+      const playerTabs = getElementById('ctl00_ctl00_CPContent_CPMain_updPlayerTabs')
+      if (!playerTabs) return
 
-      element.appendChild(span)
-    })
+      observeElement(playerTabs, () => {
+        addWeekNumbers(playerTabs)
+      })
+    }
   },
 }