Deal with under-performance fairly
If your team see you dealing with under-performance fairly then you are likely to get understanding from the team even if they may feel uncomfortable.
Team dynamics cannot be maintained if an under-performer or even a very negative team member is constantly dragging it down. If you are listening to your team, they will tell you in their own way when someone is not fitting in with the team or a problem may be brewing.
The earlier you can understand the issue and offer support to the individual the better.
Further reading on this topic can be found at: