Michael Appleton welcomed Jordan Obita to Pompey’s ranks but targeted three more players.
The Blues have recruited Reading winger Obita on loan to add another player to his options.
But Appleton is desperate to add more new men to boost his threadbare squad.
The 36-year-old is keen to speak to administrator Trevor Birch to see what he can and can’t do.
Appleton believes he is working to a budget which is among the lowest in League One.
He does expect to have Liam Walker available to face Colchester tomorrow, however.
He missed out on Saturday while waiting for international clearance to come through following his arrival.
Appleton said: ‘Liam will hopefully be ready for tomorrow and Jordan Obita will be joining us on loan from Reading this week.
‘That gets us to 17 but we need another three players to be competitive.
‘At the moment the budget is a lot smaller than suggested.
‘I would imagine it’s among the lowest in League One.
‘I’d be amazed if it isn’t in the bottom three.
‘If we pick up an injury we will be snookered.
‘Even with Jordan Obita and Liam Walker, that leaves us with 17 players.
‘It’s nowhere near enough to get through a season.
‘We need a minimum of another three players.
‘I don’t know how we are going to do it or where the money will come from but we need to find it.’
Appleton believes Obita will be an impressive addition.
He said: ‘Jordan’s an exciting player who can play as a striker or out wide.
‘He’s a runner who likes to get in behind teams.
‘He’s an exciting one who fits into our budget.’