George Thorne heads a trio of loan signings set to arrive at Fratton Park today.
The West Bromwich Albion midfielder has moved on an emergency loan ahead of the 5pm deadline.
He is joined by Hawthorns team-mate Joe Mattock – a left-back.
Michael Appleton is also hoping to tie up a third unnamed arrival before the deadline expires.
The finishing touches are currently being put to that deal.
The Pompey boss had spoken publicly of his determination to bring three new players into his squad.
That was in the aftermath of an abject 2-0 defeat at Watford last weekend.
Now he has sealed loan deals for attacking midfielder Thorne and former England under-21 defender Mattock.
Both will go straight into the squad for Saturday’s visit of Leicester. And Appleton is hopeful they will be joined by a third player.
He said: ‘I wanted to bring in some younger players.
‘There is a lot of experience in the side but I think a few more younger players will help the squad.
‘I believe some younger legs in the side will help.
‘We have been working very hard on bringing some loan players in and two are already done.
‘Hopefully a third will also be sorted before today’s deadline.’
Thorne made his Baggies debut in November 2009 at the age of just 16 years and 328 days.
The England under-19 international has gone on to make five first-team appearances in total.
Roy Hodgson pulled him out of the England under-20 squad in the summer to spend the whole of pre-season training and playing with the first team.
The 18-year-old has subsequently made the Baggies’ starting line-up for fixtures against Bournemouth and Everton – both in the Carling Cup.
He also appeared for nine-minutes as a substitute against Arsenal earlier this month, Appleton’s last game with the Baggies before taking up the Fratton hot seat.
Mattock joined West Brom from Leicester in August 2009 in a £1.2m deal.
He went on to become a regular in the Baggies’ promotion-winning side that season, totalling 34 appearances in all competitions.
But the 21-year-old fell out of favour last term and didn’t make a single appearance, instead being loaned to Sheffield United for the second half of the campaign.
He played 13 games for the Blades but couldn’t prevent relegation to League One.
Mattock has made two appearances this season, both in the Carling Cup.