Tom Davies has been linked with a move to Tranmere.
Reports suggest the defender is one of Rovers boss Micky Mellon’s main targets.
Out-of-favour Davies joined the Blues from Accrington last summer but made just 16 appearances in all competitions in the 2016-17 season.
Pompey are closing in on Swindon’s versatile captain Nathan Thompson, who can play centre-back.
National League side Tranmere also signed Ben Tollitt from the Blues last September on loan before the Liverpudlian moved to Prenton Park on a permanent basis in December.