Pompey have beaten off competition from Charlton Athletic to sign Finnish defender Petri Pasanen from Ajax on loan until the end of the season.
Addicks boss Alan Curbishley was the favourite to sign the 23-year-old, who has fallen out of favour at the Amsterdam Arena this season, but Redknapp got his man within 24 hours of the opening of the transfer window.
Pasanen is not eligible to play in today's FA Cup third round tie against Blackpool at Fratton Park but could be in the squad for the trip to Aston Villa on Tuesday night.
Redknapp said: "Petri was playing Champions League football for Ajax for most of last season and is an international for his country. He can also play as a full back so offers me the versatility I need with such a small squad."
Chairman Milan Mandaric said: "We're looking at three or four players, a goalkeeper, a midfielder and a striker with the possibility of an additional defender. What Harry Redknapp needs now is experienced players who can help immediately."
Redknapp has refused to admit any interest in Saints 'keeper Paul Jones.
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