One can use internal ssh tunneling from Remmina remote desktop client too.
If you can ssh to some linux server using ssh keys and that server have open 3389 (RDP) port for packets coming from your machine you can use following setup to RDP over ssh tunnel.
In profile editor setup the Basic tab as for direct connection. Go to SSH Tunnel tab and setup the tunelling like this:
[x] Enable SSH tunnel
(o) Custom [ip/hostname of ssh/linux server]
User name: [username on the ssh/linux server]
(o) Public key (automatic)
Using those options Remmina opens
ssh -L 3389:[target windows server]:3389 [linux server] -N
and then connects the RDP session throug that ssh channel.
If you logon to the linux server using username/password or if you are using different identity file you have to change the SSH Authentication section of profile setup.