Matt Clarke has been ruled out for the first month of this season.
And Nathan Thompson will not be fit for four to six weeks.
Clarke limped out of Pompey’s 6-0 thrashing of the Hawks last week with a groin problem when the game was at a stalemate.
After missing the start of last season through injury, the former Ipswich defender will again be absent for the Blues’ curtain-raiser.
Fellow defender Thompson, who moved to Fratton Park this summer from Swindon, has a foot problem but will be back before Clarke.
Pompey boss Kenny Jackett admitted both injuries big blows.
He said: ‘Nathan Thompson will be back before Clarke.
‘Matt will probably miss a month of the season with a groin injury.
‘It’s frustrating for him and for us because he has started well and looks a good player.
‘A lot of his rehab period is during pre-season and he won’t miss too many games, but he certainly will miss the start of the season.
‘Nathan is out for four to six weeks. We’re hoping to reduce that, but then he will not have done any training.
‘Before he does come back, the injury needs to be cleared up. Once he is back, we will push him hard.’