Both sides of the Old Firm have been linked with the former Middlesbrough man, but with Celtic on the verge of signing defenders Andreas Hinkel and Coelho, the opportunity has arisen for Walter Smith to make his move.
Rangers are on the lookout for a left-back with Stevie Smith recovering from long term injury and Sasa Papac failing to win over the fans.
Smith confirmed they were in the market: "There's no point in us bringing in anyone just to pad out the squad, but we need to strengthen."