The right-back missed Thursday's Carabao Cup defeat to Brighton. He was cup-tied, having represented Accrington in the competition before his £200,000 move to Fratton Park.
Johnson likely to replace James Bolton in defence.
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The centre-back suffered a dead leg and was earmarked to train with the Blues on Friday.
If Whatmough is fit then it's likely Paul Downing will drop out of the match-day squad as Bolton will serve as both right-back and centre-half cover.
Michael Jacobs is expected to be involved at Spotland. The new arrival was a surprising omission at Brighton, with Jackett wanting the forward to have a full week's training under his belt, having not played any games during pre-season.
Lee Brown may also be recalled to the starting XI after Cameron Pring featured at the Amex.
Meanwhile, Stephen Humphrys is in line to make his second debut for the Dale.
The striker returned to Spotland for an undisclosed fee from Southend earlier this month, having had a loan spell at the club earlier in his career.
Ryan McLaughlin is challenging to come back into Brian Barry-Murphy's side after being rested for their Carabao Cup loss to Sheffield Wednesday.
Former Pompey-linked midfielder Olli Rathbone is primed to start.
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