Lassana Diarra and Richard Hughes are both struggling to make Saturday's game having been struck down by injury.
Diarra has been with France's medical staff during the past week after picking up a knee problem in the victory at Vitoria Guimaraes.
The Blues are now waiting for him to return to Fratton Park to assess the extent of the complaint.
>>> Is Davis on his way out of Pompey? - Burton's Banter - Click here to read the latest post.Meanwhile, Hughes has gone down with a groin strain picked up in training last week.
The long-serving midfielder, who has re-established himself in the side of late, started his rehabilitation in the gym yesterday.
But he faces a battle to declare himself fit in the build-up to the trip to Villa Park.
It's a big blow to Harry Redknapp with the duo on song, impressing during Pompey's eye-catching form.
Diarra has been untouchable in the heart of the midfield, maintaining his sizzling displays of last season.
Hughes has now started Pompey's past four matches in all competitions, having failed to make a squad for the first seven matches of the season.
It leaves Sean Davis and Papa Bouba Diop as the prime candidates to replace them should they fail to recover in time.
On the plus side, John Utaka is making encouraging progress after tearing his hamstring.
The winger was back working outside at the tail-end of last week and could return to full training before this week is out.
It gives the Nigerian an outside chance of making the bench for the clash with fellow high-fliers Villa.
Never miss a Portsmouth FC story... Get them sent straight to your e-mail inbox.... click here to subscribe.
The full article contains 310 words and appears in The News newspaper.