Many managers struggle to deal with an unexplained absence that also affects employees' ability to fulfil role requirements and feel there is nothing they can do. The reality is you do not have to accept people being off without a good reason. You can investigate an employee's capability to work if they do not seem to be able to perform at the right level without a valid reason as long as what you do is proportionate, documented, fair and consistent with actions taken in same/similar cases. Points to also consider:

• are there any underlying management issues that could be a contributory factor in this person illness?
• could the employee have an underlying condition that you simply do not know about?

Look at things with an open mind, seek a professional medical opinion and investigate the matter properly as part of a formal process.