One of the most important responsibilities of an effective manager is to help their employees achieve the best results possible. In doing this, you will need to point out potentially undesirable behaviors in your staff. Some people lack strong oral communication skills, and if this shortfall is causing problems with a person's performance, you need to find a way to help this person communicate more clearly and effectively. The only other option is to find another employee, and that might not always be the most desirable outcome.
Document specific instances that you have observed where an employee needs to improve his verbal communication. When you talk to your employee to inform him of the need for improvement, use specific instances that you can recount quickly and in detail to illustrate the need for improvement.
Meet with the employee individually. You should have this meeting in a conference room or an office away from any other employees. Try to arrange for the meeting to take place at a time when you are not likely to be interrupted and can give the employee your full, undivided attention.
Tell the employee directly that he needs to improve his style of verbal communication. Tell him the specific instances in which you have noted problems with his verbal communication style, and how he could have communicated more clearly in those situations. Be prepared for the possibility that the employee has no idea that their skills are not up to your standards. The employee might turn hostile and place blame on others, including you. Keep the attention where it needs to be, on your employee's need to improve.
Create a plan that allows the employee to take specific actions to improve his verbal communication style. It is good to get the employees input on the types of assistance that he will need to improve his communication style. Consider public speaking classes for the employee, or specific business training on communications. Show that you are willing to assist your employee in improving his communication style to meet your standards.
Keep your employee accountable for following the plan and working toward improvements in the areas needed. Observe instances where the employee has used a better style of communication, and make sure that you tell him that you have noticed. Continue to point out areas where the employee is struggling in verbal communications, along with better ways to communicate. Reward an employee's success in following the plan and improving his performance.