An employee who starts missing deadlines, regularly arrives late or becomes increasingly withdrawn from colleagues might understandably raise concerns among their managers. In many workplaces, the next step would be to consider a performance improvement plan or, depending on the circumstances, formal disciplinary proceedings.

But what happens when the behaviour being addressed is actually a symptom of an underlying mental health condition? And, perhaps more importantly, what if the employer already has reason to suspect that something is wrong?

This is where businesses need to tread carefully. While employers are entitled to expect their staff to meet certain standards, following established performance management procedures does not automatically protect them from a potential discrimination claim.

Under the Equality Act 2010, a mental health condition can constitute a disability if it has a substantial and long-term adverse effect on someone’s ability to carry out normal day-to-day activities. Where an employer knows, or could reasonably be expected to know, that an employee has a disability and is likely to be placed at a substantial disadvantage, it has a legal obligation to make reasonable adjustments.

Crucially, an employee does not necessarily need to have received a formal diagnosis or explicitly identified themselves as disabled for those responsibilities to arise.

Consider someone who has previously performed well but begins struggling with their workload. They might mention to their manager that they are experiencing anxiety, feeling overwhelmed or having difficulty concentrating without formally requesting support from HR. If their performance subsequently declines, the employer could find itself in a difficult position if it proceeds directly to disciplinary action without making appropriate enquiries.

The same applies to conduct. Increased irritability, disengagement or repeated lateness may be interpreted as an attitude problem but could also be connected to an underlying condition. An employer that is aware of these difficulties cannot simply ignore that information because the employee has not formally disclosed them.

Of course, managers are not medical professionals, nor should they be expected to diagnose their staff. Not every employee experiencing stress or poor mental health will meet the legal definition of disability and it is acknowledged that most jobs will involve a degree of stress. However, where there are reasonable grounds to suspect that a condition may be affecting someone’s ability to work, employers should be prepared to explore the situation before making decisions that could have serious consequences.

That might involve seeking occupational health advice, discussing possible adjustments with the employee or reconsidering how existing performance expectations are applied. Changes to working hours, workloads or deadlines could be appropriate, while adjustments to the disciplinary or capability process itself may also be necessary.

For example, an employee experiencing severe anxiety may need additional support during formal meetings, while rigid attendance requirements could place someone attending regular therapy appointments at a disadvantage. What constitutes a reasonable adjustment will depend on the circumstances, but applying an identical process to every employee is not necessarily the same as treating them fairly.

There is also a wider issue for businesses that have invested in workplace wellbeing policies but have not given sufficient consideration to how these policies operate in practice.

It is often line managers, rather than HR teams, who first become aware that an employee is struggling. A passing conversation about anxiety or repeated mentions of feeling overwhelmed might not immediately prompt a formal response, but such information could become relevant if the employer later needs to demonstrate what it knew about an employee’s condition and when.

Having a comprehensive mental health policy offers little reassurance if managers do not understand when to act on concerns or how those concerns should inform decisions about performance and conduct. Training therefore needs to go beyond recognising the signs of poor mental health and equip managers to understand when additional enquiries or adjustments may be necessary.

None of this means that employees experiencing mental health difficulties are exempt from performance management. There will be situations where, despite appropriate support and reasonable adjustments, an employee remains unable to fulfil the requirements of their role. Employers can still take action, but they need to be able to demonstrate that their decisions were properly considered and that their legal obligations were addressed.

Keeping a clear record of conversations, adjustments considered and the reasoning behind any subsequent action is particularly important. Without that evidence, defending a discrimination claim can become considerably more challenging.

As businesses continue to scrutinise performance and attendance, there is a danger that the focus on addressing underperformance overshadows the factors contributing to it. For HR professionals, the question should not simply be whether an employee is meeting expectations, but whether there is information the business ought to consider before deciding what happens next.

After all, an employer may believe it is following its disciplinary procedures to the letter, only to discover that the problem was not the employee’s performance, but its own failure to consider what was behind it.

Graham Millar is employment law partner at Gilson Gray