Former Hearts captain Marius Zaliukas trained with Rangers on Thursday.
The 29-year-old Lithuanian international is a free agent, having left Hearts in the summer.
Zaliukas made more than 200 appearances for Hearts in seven years and scored 14 goals for the Edinburgh club.
Rangers signed Bilel Mohsni this summer, while Emilson Cribari, Sebastien Faure, Chris Hegarty and skipper Lee McCulloch can also play in central defence.
The Ibrox club have long been linked with Bosnian international Boris Pandza but talks have proved fruitless.