Pompey have signed centre-back Bondz N’Gala on a one-month contract.
The 23-year-old was on trial with the Blues earlier in the summer and played in the 5-0 friendly victory at Havant & Waterlooville.
He has been without a club since leaving Stevenage at the end of last season.
N’Gala began his career with West Ham, but made just a single senior appearance and had several loan spells before joining Plymouth in 2010.
He made a total of 37 appearances for the Devon club before spending a season at Yeovil and then joining Stevenage last summer, playing 28 times for Boro.