As a new manager, you understand that to succeed you need to build a team that functions well together. Team members must support each another collectively and perform as individuals. If you suspect that you have a team member who is not performing up to par, do you have what it takes to take care of the problem?
First you need to evaluate the situation. Give your apparently poor performer a test assignment. Experts in action learning for leadership development say this is a good way to quickly and accurately assess their capabilities and willingness to do the job. Buttress your observations by checking in with their team mates, subordinates and former supervisors.
If you decide that there is little hope that the team member can measure up to the level of performance you need, it is time to help them find another position. It is never easy to let someone go. But your responsibilities now as a manager is to your team and ultimately to the organization.