If employees are off work for 28 days or less, they do not need to give their employer a fit note or other proof of sickness from a medical professional.
When they return to work, their employer can ask them to confirm they’ve been off sick. This is called ‘self-certification’. The employer and employee will agree on how the employee should do this.
Employees must give their employer a doctor’s ‘fit note’ if they’ve been ill for more than 28 days in a row and have taken sick leave. This includes non-working days, such as weekends and bank holidays.
Here is a link to the government website for further information – https://www.gov.uk/taking-sick-leave