Tom Davies and Jack Whatmough have been challenged to fill the gulf created by Matt Clarke’s injury.
The central defender is expected to miss Pompey’s League One kick off through a groin problem.
Clarke was forced off with the issue after 16 minutes of last weekend’s friendly at the Hawks.
Assistant boss Joe Gallen now does not anticipate the defender being available for the August 5 curtain-raiser against Rochdale.
Fellow defender Nathan Thompson is already sidelined, with a foot injury claiming him during his second training session with the club.
That leaves Davies and Whatmough to scrap it out to partner Christian Burgess at the heart of the Blues’ back four.
It’s tough to say how long because you never really know, but I believe Matt will miss the start of the season, put it that wayJoe Gallen
Gallen said: ‘There are people who can fill the role.
Tom Davies has looked pretty good and Jack Whatmough played the other night.
‘Matt has an injury to his groin so we are very disappointed about that and we believe he is going to be out for some time.
‘It’s tough to say how long because you never really know, but I believe he will miss the start of the season, put it that way.
‘He visited a specialist yesterday. Those results will give us more of a rounded view on it.
‘If I put a time on it maybe it would be a mistake, but I don’t think he will make the start of the season.
‘In his words, he went to stretch and it went “pop”. Pop is not a good word.
‘We are disappointed because he is a really good player and has proven that so far, even in the few weeks we’ve had him.’
Davies came off the bench to replace the injured Clarke in the 6-0 victory over the Hawks.
He received the nod ahead of Whatmough, who instead saw out the final 18 minutes of that Westleigh Park fixture.
At Poole Town on Tuesday night, a Pompey XI consisted of Whatmough and first-year professional Theo Widdrington at the heart of the defence.
Davies was instead rested, along with those who started that Hawks fixture.
Clarke and Burgess forged an outstanding central defensive partnership in the Blues’ charge to the League Two title last term.
As the season progressed, Whatmough established himself as their understudy – ahead of Davies.
Indeed, Davies has attracted interest from Tranmere this summer after appearing to have fallen out of favour at Fratton Park.
Now the 25-year-old has edged closer to a Pompey first-team return.
Gallen added: ‘There are enough players around to fulfil that position and still make us strong – and I still think we can start the season well and win some games.
‘Tom and Jack are in the thinking, it’s now up to them to step into Matt Clarke’s position.’