A computer-assisted teleoperated system includes a pre-load assembly in an instrument manipulator that is under the control of a controller. The controller can automatically cause the preload assembly to engage and disengage a preload. A surgical apparatus includes an instrument manipulator assembly and a sterile adapter assembly. The sterile adapter assembly is mounted in the distal face of the instrument manipulator assembly. When the preload assembly configures the instrument manipulator assembly to apply a preload force on the sterile adapter assembly, the sterile adapter assembly is removable from the distal face of the instrument manipulator. The sterile adapter assembly includes a mechanical sterile adapter assembly removal lockout and a mechanical instrument removal lockout.