Warning: require(../app/functions.php): failed to open stream: No such file or directory in /work/web/index.php on line 3

Fatal error: require(): Failed opening required '../app/functions.php' (include_path='.:/usr/local/lib/php') in /work/web/index.php on line 3

このようなエラーが出てきました。
どうすれば良いでしょうか？