Wales Assistant Manager John Hartson says his side must improve following a dismal performance against Serbia last month.
Wales lost 6-1 to their rivals and suffered an enormous setback in their bid to reach the 2014 World Cup.
John Hartson told journalists: "It wasn't good enough."
Wales play Scotland at the Cardiff City Stadium tonight in a game they must win to keep alive any hope of qualifying for the 2014 World Cup.
Wales assistant manager John Hartson believes Friday's World Cup qualifier against Scotland is a make or break game.