The Scot has been an unused substitute in the Blues’ past two matches against AFC Wimbledon and Northampton.
Naismith, 25, was Pompey’s talisman in the second half of last season.
He amassed nine goals from 15 appearances as the Blues secured the League Two title on a dramatic final day of the campaign, following a 6-1 thrashing of Cheltenham at Fratton Park.
But the Rangers Academy product has made just four starts in all competitions this term, including a goalscoring display in the 3-3 draw against Fulham under-21s in the Checkatrade Trophy.
Jackett was tempted to bring on the forward in the second half of Pompey’s 3-1 defeat at Northampton on Tuesday night to try to salvage a result.
However, he opted not to – with Ben Close being his only substitution.
But the Fratton Park boss believes Naismith still has a key role to play and is providing strong competition to his regular front men.
Jackett said: ‘I was tempted to bring on Kal but I didn’t want to take Brett Pitman, Conor Chaplin or Matty Kennedy off.
‘Chaplin and Pitman have been ahead of him, while we have brought Oliver Hawkins in.
‘At the moment, he is after one of the two forward positions, as well as the wide left position where we have Kennedy and Kyle Bennett.
‘For Kal there is some competition around there.
‘Having said that, having that competition is a good thing.
‘If they do not produce or get the goals then I have a good player who is able to come in.’