Elective surgeries such as knee replacement operations and cataract surgery are seen as a valid reason for being absent from work by only 35% of employers, research for AXA PPP has found.
The research also found that 42% of managers agreed flu was a serious enough reason for an employee to be absent, and 39% saying back pain was serious enough to be absent.
A migraine was considered a reason for being absent from work by 22% of managers surveyed.
Almost a quarter 23% of employees won't tell their line manager the real reason for their absence when calling in sick as they're afraid of being judged.
The findings come from an online survey of 1000 senior business managers, MDs, CEOs and owners, along with 1000 non-executive employees was undertaken by OnePoll for AXA PPP healthcare.
Not being believed was cited by a further 15% of employees as a reason for not giving the real reason for absence from work.
Employees were much more likely to lie about the cause of sickness if it was due to mental health, 77% would tell the truth if their sickness was due to a physical ailment, compared to 39% for stress anxiety or depression.
Employees working in SMEs with less than 250 employees were less likely to tell their line manager they were taking time off for stress, anxiety or depression.
Of those working for larger companies 44% would tell their boss if they were off for stress anxiety or depression, while 37% of those working in SMEs would do the same.
Glen Parkinson, SME director for AXA PPP healthcare, said: "With managers showing so little understanding of or support for employees suffering from illness, it's not difficult to see why employees worry about phoning in sick.
"Employers need to challenge this blinkered attitude, both for their own benefit as well as that of their employees.
"In many cases it is more productive for an employee to take a day off to recover from a spell of illness rather than to come into work, with diminished productivity and, for likes of colds and flu, the potential to spread their illness to workmates.
"Employers need to trust employees to take the appropriate time off sick and, where practicable, consider allowing them to work from home.
"Showing sympathy and flexibility when employees are unwell is crucial to maintaining a healthy and committed workforce, which in the long term creates a healthier business."