Microsoft : How to disable RDP access for Administrator

Solutions:

To deny a user or a group logon via RDP, explicitly set the "Deny logon through Remote Desktop Services" privilege.

• Start | Run | secpol.msc if editing the local policy or chose the appropriate policy and edit it
• Go to -> | Local Policies | User Rights Assignment.
• Find and double click -> "Deny logon through Remote Desktop Services"
• Add the user and / or the group that you would like to dny access.
• Click ok

Source : 

• https://support.microsoft.com/en-us/help/2258492/you-notice-that-the-check-box-deny-this-user-permissions-to-logon-to-a