Curtis Main has been ruled out for the next two weeks with a hamstring injury.
The Pompey striker started last weekend’s 1-0 win against Gillingham and his header which crashed against the post lead to Matty Kennedy’s strike shortly after the restart.
But the former Doncaster Rovers man has picked up a hamstring complaint and missed today’s 2-0 win against MK Dons.
Blues boss Kenny Jackett said: ‘It’s unfortunate for him. He tells me it’s a similar situation to what happened last season.
‘But he’ll only be out for a couple of weeks and he’ll be back.’