Jack Whatmough is pencilled in for a December return.
The central defender suffered knee cartilage damage against Doncaster in February, immediately sidelining him for the long-term.
It was a cruel blow to the Gosport youngster, who at the time was producing the best form of a Pompey career hampered by injury.
Establishing himself as a regular ahead of Christian Burgess, Whatmough had this season made 30 appearances when the set-back occurred.
Now he is challenged with battling back from a third serious injury to his left knee.
The 22-year-old was able to throw away his crutches a fortnight ago as he maintains rehabilitation.
And Kenny Jackett is anticipating Whatmough’s comeback arriving around the turn of the year.
He said: ‘Jack is coming on, his determination is very good.
‘I don’t think he’ll be back in pre-season, instead it will be at some stage during the course of mid-winter, that’s how it looks.
‘Around the turn of the year perhaps, common sense tells you that will be the case.
‘It’s a path he has trodden before, but Jack is a very positive lad and whatever deadline you give him he will be working hard to try to beat that.
‘It’s about getting mobility into the knee and building up leg muscle, which obviously gets affected by operations quite badly.
‘I don’t think you forget about him on a human level, but in terms of first-team selection he is obviously not under consideration because of the injury.
‘Jack’s a positive lad anyway, I don’t think there's much which will overcome him or knock him back, his morale is very good.’
Whatmough has made 96 appearances and scored once since making his Pompey debut against Southend in November 2013.