Pompey will assess the extent of Lee Williamson’s injury over the next 24 hours.
The midfielder limped out of last night’s 2-2 draw with Colchester in the 33rd minute with a hamstring problem and was replaced by Adam Webster.
It was a worrying sight for Blues fans, with the 30-year-old still feeling his way back to fitness having spent the summer without a club.
Williamson was substituted in the 62nd minute against Bournemouth last weekend as the club look to ease him back into regular football.
Now Michael Appleton admitted he is concerned over last night’s problem, which forced the ex-Sheffield United man off within minutes of his side taking the lead.
And he is hoping to soon discover whether Williamson can feature in Saturday’s visit to Carlisle.
He said: ‘Lee just felt a little bit of a tweak in his hamstring so we didn’t want to take any chances with him.
‘We got him off as quickly as we possibly could and with hamstrings you can’t tell until 24-36 hours later how he is.
‘There are a lot of games coming up so we didn’t want to risk him.’
Williamson scored 13 goals in 49 appearances for Sheffield United last season.
Appleton described his Fratton Park arrival as capturing ‘probably’ the best player in League One football last term.
His partnership with Brian Howard in the centre of midfield is going to be crucial to the Blues’ campaign.
In his injury absence last night, Liam Walker moved into a central position and impressed. The 24-year-old will deputise once more should Williamson fail to recover for Carlisle.
However, Appleton is keeping his fingers crossed the ex-Watford man’s problem is not as bad as first feared last night.