Steve Cotterill has revealed he expects to bring in just one emergency loan signing.
The window opened for those clubs outside of the Premier League yesterday, allowing additional players to be recruited on loan.
Lasting until November 24, it promises to be a busy period.
Pompey are among those looking to strengthen, with a squad currently numbering 19.
However, Cotterill admits his budget dictates there is likely to be one fresh arrival.
Under new owners CSI, the Blues have already brought nine players to Fratton Park since the summer.
That includes costly outlays on the likes of Greg Halford, Luke Varney and Erik Huseklepp.
Pompey’s boss remains tight-lipped on his emergency loan window targets.
He has been heavily linked with a move for Aston Villa’s versatile right-sided youngster Chris Herd.
Stoke’s Ryan Shotton, Danny Pugh and Michael Tonge have also been mentioned.
But at this stage, Cotterill anticipates bringing only one player to the south coast in the current window.
He said: ‘The emergency loan window is open now and it’s not a foregone conclusion that something is going to happen.
‘We probably have enough money in the budget to bring in one loan signing.
‘It means that player has to be, for me, pretty flexible.
‘The owners have backed me this summer. They’ve spent money and I thank them for that.
‘Now, at this moment in time, what we have remaining in our budget is enough for one emergency loan. So that’s what we are looking at.
‘I have somebody in mind from a Premier League club.
‘But I would say, at present, we are not close because the player has just got in to the first team.
‘We will have to wait and see how that one develops.’
The emergency loan window has already seen Lewis Stockford departing for Salisbury for a month.
But it is the arrival of a new signing which Blues fans are eager to see happen.
Herd’s name has been regularly linked with Pompey since the January transfer window.
The 22-year-old Australian international can play either on the right-hand side of midfield or at right-back.
Following the sale of right-back Luke Young to QPR, Herd was named in Villa’s starting line-up for their last match against Wolves.
Since then, Alex McLeish has recruited Scotland defender Alan Hutton from Spurs.
Both players are in the squad for tomorrow’s trip to Everton.
Meanwhile, rumoured Blues target Shotton has made five substitute appearances for Stoke so far this season.
The full-back scored a late winner against West Brom in their last match before the international break.
Pugh and Tonge were among five players made available for loan by Potters manager Tony Pulis earlier this week.
Pugh, a left-sided midfielder or defender, has made four appearances for Stoke this season, including an outing in the Europa League.
Tonge, who can operate on the right-hand side of midfield and in the centre, has not made a Stoke squad during the current campaign.