Gabor Gyepes has joined Pompey on a one-month deal.
The 31-year-old defender trained with the Blues last term without earning a contract.
Michael Appleton has now decided to bring the Hungarian on board, however, he will need international clearance to feature at Crawley on Sunday.
Gyepes, who has 26 international caps, spent four years at Cardiff City after spells with Northampton Town and Wolves.
Having started his career at Ferencvaros, he has been with Hungarian outfit Vasas for the past few months.
Appleton is keen to add experience to the heart of his defence, to help young centre-backs Kevin Long and Josh Thompson.