Call to undefined function making site unavailable After making a Backup/Migrate copy of source site files, the very source site for unknown reason broke down with this error:


  Fatal error: Call to undefined function link_field_property_info_callback() in /sites/all/modules/entity/modules/field.info.inc on line 30


Most probably it comes from references to the Link module.
I have googled around, but the solutions good for others are not for me, as I cannot access admin to un-install the module. Is there anything I could do here without Drush?

I really do not quite understand the origin of that situation, but I would more like to focus on resolving the effect.
You can try to (re)move the faulty module's directory, at least temporarily. It should prevent the call and let you access the necessary admin pages.