SINGAPORE - Are you present physically but mentally absent from your job? Then you are a zombie employee - and more than half of businesses here have been infected.

According to research by specialist recruiter Robert Half, 57 per cent of Singaporean businesses have workers who are suffering from "inner resignation" - staff seemingly going about their work but mentally checked out and sleepwalking through the work day.

"The working dead" are twice more likely to be found in medium-sized and larger companies - with 68 per cent saying they have them - versus 32 per cent for small businesses, said Robert Half.

Said David Jones, senior managing director of Robert Half Asia Pacific: "Inner resignation is often overlooked by employers, especially in workplaces where employees are left alone to get on with their job. Employers need to be more vigilant in looking for signs that an employee is mentally disengaged, such as a lack of motivation for bonuses or advancement or a drop in productivity."

Zombies workers are not just found in Singapore. A 2013 Gallup poll found that 70 per cent of American workers were not engaged or actively disengaged from work which means they were essentially emotionally disconnected from the company and the people they work with, Forbes magazine reported. More shocking - Gallup estimated that that high a level of disengagement costs the US between US$450-$550 billion each year.

Robert Half, which surveyed 100 chief financial officers (CFO) and finance directors in Singapore for its study, pointed out strategies businesses can use to fight the zombification of their workplace such as employee recognition and encouraging open communication.

"To reduce the risk of inner resignation, employers need to keep the lines of communication open with their staff so that the employees feel confident they can raise their concerns without fear of reprisals," said Mr Jones. "If workplace concerns are responded to early, then there is less chance of employees becoming disengaged from their work."

He said employees must also take responsibility for their satisfaction at work.

"If an employee finds they have accepted inner resignation, then they should identify the cause of their dissatisfaction and raise the matter with their employer during their performance review. If the issue cannot be resolved then they are better off seeking a new job than lingering in a role they are unhappy with," said Mr Jones.