Celtic manager Ronny Deila insists Virgil van Dijk does not want to leave the Scottish Premiership leaders in January.
Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
The 25-year-old was one of the mainstays of Southampton's promotion campaign last season, but he has found first-team opportunites limited since the Saints entered the top flight.
The Belgian has been restricted to just seven appearances in all competitions this season, although he has featured in four games since the turn of the year.
De Ridder, who spent three years with Dutch side De Graafschap before moving to Southampton in the summer of 2011, becomes Dougie Freedman's fifth signing of the transfer window.