James Wesolowski has been brought in on loan from Leicester with the initially deal running to January with the option to extend it to next summer.
Rubiales spent the 2008/09 season at Alicante and impressed at a recent trial with the club.
Manager Billy Reid still hopes to add to his squad however.
“I basically had a team of trialists in Ireland last week and we have a lot of work to do to get the squad ready,” he said in the Daily Record.
