If you think that a member of your team is not performing to the required standard, it is better for both of you if the issue is addressed early.
In the first instance, performance issues should be dealt with informally. The aim is to resolve the concern before positions harden or patterns of working become entrenched and therefore becomes harder to change and/or starts to impact on other team members. As with all types of performance issues, it is important that the employee has the opportunity to respond and improve before any formal action is taken.
There are a number of things you should do during an informal discussion (whether as part of regular 1:1 meetings or arranged specifically to address poor performance) - to help you a checklist has been developed.
If any mitigating circumstances are identified they may need further exploration and consideration. For example, a newly raised disability disclosure or medical issue may require a referral to Occupational Health.
REMEMBER: keep a note of the meeting and of the required outcomes, targets and timescales for improvement and share it with the individual after the meeting.