I would say it depends on your type of virtual disk - VHDX is new to Windows 8 and Windows Server 2012. If you created your virtual machine using a vhdx disk format, it definitely won't migrate to 2008 R2.
Then it depends on the configuration of the VM (if you've exceeded the specs of a VM on 2008 R2 with the config of Win8, then you'll probably have to change the settings or possibly re-create them.
You won't be able to just move the VM. If, as the other response says, you use the VHD rather than VHDX file format, you can move the virtual disk. It will help if you don't install the integration components in the VM, or if you uninstall them before the move.
I would say it depends on your type of virtual disk - VHDX is new to Windows 8 and Windows Server 2012. If you created your virtual machine using a vhdx disk format, it definitely won't migrate to 2008 R2.
Then it depends on the configuration of the VM (if you've exceeded the specs of a VM on 2008 R2 with the config of Win8, then you'll probably have to change the settings or possibly re-create them.
You won't be able to just move the VM. If, as the other response says, you use the VHD rather than VHDX file format, you can move the virtual disk. It will help if you don't install the integration components in the VM, or if you uninstall them before the move.