diff --git a/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.test.tsx b/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.test.tsx
new file mode 100644
index 0000000000..fbcac5c892
--- /dev/null
+++ b/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.test.tsx
@@ -0,0 +1,60 @@
+import { fireEvent, screen } from '@testing-library/react';
+import { render } from 'utils/testRenderer';
+import { vi } from 'vitest';
+import { AvatarCell } from './AvatarCell';
+
+test("the filtering button should have aria-disabled='true' when the user id is 0", async () => {
+    const Cell = AvatarCell(() => {});
+    render(<Cell row={{ original: { createdBy: { id: 0, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+    expect(button).toHaveAttribute('aria-disabled', 'true');
+});
+
+test("the filtering button should have aria-disabled='false' when the user id is not 0", async () => {
+    const Cell = AvatarCell(() => {});
+    render(<Cell row={{ original: { createdBy: { id: 1, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+    expect(button).toHaveAttribute('aria-disabled', 'false');
+});
+
+test('the onAvatarClick function should not be called when the user id is 0', async () => {
+    const onAvatarClick = vi.fn();
+    const Cell = AvatarCell(onAvatarClick);
+    render(<Cell row={{ original: { createdBy: { id: 0, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+
+    fireEvent.click(button);
+
+    expect(onAvatarClick).not.toHaveBeenCalled();
+});
+
+test('the onAvatarClick function should be called when the user id is not 0', async () => {
+    const onAvatarClick = vi.fn();
+    const Cell = AvatarCell(onAvatarClick);
+    render(<Cell row={{ original: { createdBy: { id: 1, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+
+    fireEvent.click(button);
+
+    expect(onAvatarClick).toHaveBeenCalled();
+});
+
+test("when the user id is 0, the tooltip should tell you that you can't filter by unknown users", async () => {
+    const Cell = AvatarCell(() => {});
+    render(<Cell row={{ original: { createdBy: { id: 0, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+    fireEvent.mouseOver(button);
+
+    const tooltip = await screen.findByRole('tooltip');
+    expect(tooltip).toHaveTextContent("can't filter by unknown users");
+});
+
+test("when the user id is not 0, the tooltip should not tell you that you can't filter by unknown users", async () => {
+    const Cell = AvatarCell(() => {});
+    render(<Cell row={{ original: { createdBy: { id: 1, name: '' } } }} />);
+    const button = await screen.findByRole('button');
+    fireEvent.mouseOver(button);
+
+    const tooltip = await screen.findByRole('tooltip');
+    expect(tooltip).not.toHaveTextContent("can't filter by unknown users");
+});
diff --git a/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.tsx b/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.tsx
index 3552d830d9..d299ed68dd 100644
--- a/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.tsx
+++ b/frontend/src/component/project/Project/PaginatedProjectFeatureToggles/AvatarCell.tsx
@@ -1,6 +1,5 @@
 import { type Theme, styled } from '@mui/material';
 import type { FC } from 'react';
-import { visuallyHiddenStyles } from '../CreateProject/NewCreateProjectForm/ConfigButtons/shared.styles';
 import { ScreenReaderOnly } from 'component/common/ScreenReaderOnly/ScreenReaderOnly';
 import { HtmlTooltip } from 'component/common/HtmlTooltip/HtmlTooltip';
 import { UserAvatar } from 'component/common/UserAvatar/UserAvatar';
@@ -32,23 +31,34 @@ const StyledAvatarButton = styled('button')({
     padding: 0,
 });
 
-export const VisuallyHiddenButtonText = styled('span')(() => ({
-    ...visuallyHiddenStyles,
-    position: 'absolute',
+const StyledSecondaryText = styled('p')(({ theme }) => ({
+    color: theme.palette.text.secondary,
 }));
 
 export const AvatarCell =
     (onAvatarClick: (userId: number) => void): FC<AvatarCellProps> =>
     ({ row: { original } }) => {
+        const ariaDisabled = original.createdBy.id === 0;
+        const clickAction = ariaDisabled
+            ? () => {}
+            : () => onAvatarClick(original.createdBy.id);
+        const tooltipContent = ariaDisabled ? (
+            <>
+                <p>{original.createdBy.name}</p>
+                <StyledSecondaryText>
+                    You can't filter by unknown users.
+                </StyledSecondaryText>
+            </>
+        ) : (
+            <p>{original.createdBy.name}</p>
+        );
+
         return (
             <StyledContainer>
-                <HtmlTooltip
-                    arrow
-                    describeChild
-                    title={original.createdBy.name}
-                >
+                <HtmlTooltip arrow describeChild title={tooltipContent}>
                     <StyledAvatarButton
-                        onClick={() => onAvatarClick(original.createdBy.id)}
+                        aria-disabled={ariaDisabled}
+                        onClick={clickAction}
                     >
                         <ScreenReaderOnly>
                             <span>