Pompey aceÂ ruled out of season's kick-off
Dion Donohue is expected to miss the start of Pompey's season.
The left-sided player today returned to training having contracted Glandular fever over the summer.
However, Jackett is not anticipating having him available for selection until beyond the August 4 curtain-raiser against Luton.
Donohue, who suffered a blistered foot earlier in pre-season, has been unable to feature in any friendly action for the Blues.
And Pompey's boss remains unsure when the former Chesterfield man will be ready to play first-team football.
Jackett said: '˜Dion today didÂ some training but not a lot, though.
'˜We'll see how he recovers, how he goes andÂ how much he can do, it's trial and error really.
'˜It's hard to put a timescale on it. Is he over it?Â Is he not?Â It is one of those where we are going off what the doctors say, they say he can do a degree of work.
'˜We will see in the next 10 days how he feels and if he can build up.
'˜We hope Dion stays training with us and doesn't need any more time off, it depends how it goes and how he feels. It's not something you have a protocol on, youÂ take it day by day.
'˜But I cannot see him being ready for Luton, although I don't think he will be too long after that.
'˜I will be surprised if he makes next weekend, though.'
Donhue made 33 appearances last season and impressed after a slow start to his Fratton Park career.
From the turn of the year, he emerged as one of Pompey's most consistent performers, with only Jamal Lowe racking up more assists.
Jackett has earmarked him for consideration in his favoured central midfield role during the forthcoming season, after largely playing at left-back last term.
However, a blistered foot hampered his early pre-season, ruling him out of friendlies with Cork and the Hawks.
At that stage, despiteÂ discomfort with his foot, Donohue continued to train, working hardÂ on the club's six-day pre-season stay in Cork.
Yet, upon his return to England, it was discovered he was suffering from Glandular fever, subsequently sidelining the 24-year-old for the remainder of pre-season friendly schedule.
Crucially, Donohue remains the sole member of Jackett's squad not to have appeared in a match ahead of the new campaign.
And the precise timeframe for his return is stillÂ unclear.Â