Pompey’s medical team are assessing Joe Mason after he sustained an injury on reserve-team duty.
The Wolves loanee was forced off with a groin complaint after two minutes of this afternoon’s Central League Cup match at AFC Wimbledon.
He was replaced by Academy youngster Alfie Stanley, as Jake Wigley’s side went on to lose 4-0.
The Blues are now waiting to discover the extent of the damage to Mason ahead of Saturday’s FA Cup trip to Maidenhead.
And with just three outings so far during a loan spell scheduled until January, it represents an unfortunate setback for the attacking midfielder.
First-team coach Wigley said: ‘After a few minutes, Joe felt a tiny tweak in his groin so there was no point keeping him on.
‘We just brought him off and hope it’s nothing big. It was just a precaution really.
‘Joe seemed like he wasn’t too worried within himself and said he felt it a little bit, but it’s too early to say what it definitely is.
‘He has now gone back to the training ground to see Bob Bacic (head physio) and find out what is what after they’ve had a proper look at him.’
Mason’s sole Pompey start arrived in last month’s Checkatrade Trophy win at Crawley, when he missed a late penalty.
The 27-year-old has featured for just 10 minutes during the Blues’ table-topping League One campaign.
That came as a substitute in September’s 2-2 draw with Wycombe, with his other outing a 4-0 Checkatrade Trophy win over Gillingham, also from the bench.
Kenny Jackett has repeatedly reassured the former Cardiff forward that there are still first-team opportunities, despite his ongoing lack of action.
However, the form of Gareth Evans and Oli Hawkins, coupled with competition from Brett Pitman, has ensured Mason has found it tough to find a way past.