diff --git src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
index e741b2149d..2b2aee7bc5 100644
--- src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
@@ -891,7 +891,27 @@ class WP_REST_Users_Controller extends WP_REST_Controller {
 		}
 
 		if ( ! empty( $schema['properties']['capabilities'] ) ) {
-			$data['capabilities'] = (object) $user->allcaps;
+			/**
+			 * If the user has no role on a site of the network, make sure
+			 * to populate his capabilities with Administrator ones if he
+			 * is one of the Super Administrators.
+			 */
+			if ( ! $user->allcaps && is_multisite() ) {
+				$site_roles = wp_roles();
+				$admin_caps = array_merge(
+					$site_roles->get_role( 'administrator' )->capabilities,
+					array( 'administrator' => true )
+				);
+
+				$capabilities = array_fill_keys( array_keys( $admin_caps ), user_can( $user->ID, 'manage_network' ) );
+				$allcaps      = wp_parse_args( $user->allcaps, array_filter( $capabilities ) );
+
+			// Otherwise use user role's capabilities.
+			} else {
+				$allcaps = $user->allcaps;
+			}
+
+			$data['capabilities'] = (object) $allcaps;
 		}
 
 		if ( ! empty( $schema['properties']['extra_capabilities'] ) ) {
diff --git tests/phpunit/tests/rest-api/rest-users-controller.php tests/phpunit/tests/rest-api/rest-users-controller.php
index 7b81eb1240..6af2b6534f 100644
--- tests/phpunit/tests/rest-api/rest-users-controller.php
+++ tests/phpunit/tests/rest-api/rest-users-controller.php
@@ -996,6 +996,36 @@ class WP_Test_REST_Users_Controller extends WP_Test_REST_Controller_Testcase {
 		$this->assertEquals( rest_url( 'wp/v2/users/' . self::$user ), $links['self'][0]['href'] );
 	}
 
+	/**
+	 * @group ms-required
+	 */
+	public function test_get_current_user_ms() {
+		$this->allow_user_to_manage_multisite();
+		wp_set_current_user( self::$user );
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/users/me' );
+		$request->set_param( 'context', 'edit' );
+		$response = $this->server->dispatch( $request );
+		$data = $response->get_data();
+		$capabilities = $data['capabilities'];
+
+		$this->assertTrue( $capabilities->manage_options );
+
+		// Create a new site the SuperAdmin is not a member of.
+		$user_id = $this->factory->user->create();
+		$blog_id = $this->factory->blog->create( array( 'user_id' => $user_id ) );
+		switch_to_blog( $blog_id );
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/users/me' );
+		$request->set_param( 'context', 'edit' );
+		$response = $this->server->dispatch( $request );
+		$data = $response->get_data();
+
+		restore_current_blog();
+
+		$this->assertEquals( $capabilities, $data['capabilities'] );
+	}
+
 	public function test_get_current_user_without_permission() {
 		wp_set_current_user( 0 );
 		$request  = new WP_REST_Request( 'GET', '/wp/v2/users/me' );