That depends. Do you intend on installing the Linux boot loader on your SSD to select the boot OS, or do something like select the boot device from firmware?
If you're doing the latter, just disconnect the SSD and do the install. If the former, do a backup just in case you make a mistake during installation.
If you're doing the latter, just disconnect the SSD and do the install. If the former, do a backup just in case you make a mistake during installation.