Ross McCrorie is expected to be sidelined for up to a month.
And the hamstring tear sustained in last night’s 4-1 victory over Southend will also force him to pull out of Scotland’s under-21 squad.
The Rangers loanee departed the Fratton Park pitch on 40 minutes, to be replaced by Brandon Haunstrup in an unfamiliar right-back role.
He instantly felt his hamstring following a challenge on the touchline in front of the South stand and realised the worst.
Kenny Jackett was already without one Scot for the visit of Sol Campbell’s side, after Craig MacGillivray strained a quad in Monday’s training.
Now McCrorie could be absent for four weeks.
Assistant boss Joe Gallen said: ‘Ross will be going for a scan, but you don’t have to be an Einstein to work out he has pulled his hamstring.
‘Straight away that’s 2-4 weeks out. It depends on the severity of it, of course, but he will be out for a while.
‘As soon as you pull your hamstring, if it’s a grade one it’s 2-3 weeks, a grade two and it’s going into four weeks, so you’ve got to be careful.
‘Strangely enough, he said he has never, ever pulled his hamstring so doesn’t quite understand what it is like and how you must be careful.
‘Let’s wait for the results, but he has torn his hamstring and once you do that you are out for a couple of weeks – he won’t be going to Scotland.’
The 21-year-old is a member of Scot Gemmill’s under-21 squad for a game against Greece (November 15).