Thery Racon is set to pen a new Pompey deal initially until January.
The French midfielder has impressed during his first month back and Guy Whittingham is eager to tie him to the Blues.
The deal will also include an option for the ex-Millwall man to remain for the rest of the season.
Racon will be following Gavin Mahon and Bondz N’Gala in penning a fresh agreement during the past week as Whittingham seeks to retain his existing squad at Fratton Park.
He has made five appearances since coming back to the club last month, most recently in the 3-2 victory over Exeter at the weekend.
The 29-year-old replaced Johnny Ertl in the side to form a new-look midfield, alongside new skipper Simon Ferry.
Despite having been without a club since the end of the season, Racon has impressed during his second spell with Pompey and been an important figure in the recent improvement.
During his first spell, he was an ever-present for the Blues, making 18 appearances on loan from Millwall.
Meanwhile, Ashley Harris and Nick Awford have returned to Fratton Park – just five days after joining Chelmsford on loan.
The sacking of Dean Holdsworth as the Clarets’ manager on Monday morning prompted the Skrill South club to send the duo back.
Caretaker boss Kenny Brown has decided to focus on the players permanently at the football club and ended their loan spell.
Harris featured as a second-half substitute in their 6-0 home defeat to Boreham Wood at the weekend.
Awford was unused from the bench.
The pair had only joined Chelmsford on Thursday in the search for regular football to aid their development.