Ryan Williams has been added to Pompey’s injury list ahead of the trips to MK Dons and Gillingham.
The winger limped off injured in the opening stages of the Boxing Day victory over Wycombe at Fratton Park.
And Kenny Jackett is not expecting him to be available for selection when his side end the year at Stadium MK.
The Blues boss said: “Ryan’s picked up a very frustrating groin injury, but Marcus Harness is a strong player and will come into the side.
“I was pleased with him when he came on against Wycombe because he did well and has to turn on his best form, which can win matches.
"New Year’s Day will be too soon for him I would think, so we’ll have to see about those cup ties at Fleetwood and Walsall."
“I don’t think Ryan will be fit for these upcoming games and we have to work with the committed group we have.
“New Year’s Day will be too soon for him I would think, so we’ll have to see about those cup ties at Fleetwood and Walsall.”
Pompey have a number of other absentees for their League One fixtures either side of the new year celebrations.
Jackett said: “It’s the second time that Ross McCrorie has injured that hamstring and we can forget about him until mid-January.
“He’s a very good player – as I’ve said on many previous occasions – and it just hasn’t fallen for him here yet. We’ll persevere with him and he’ll keep going.
“It’s also going to be a number of weeks until we have either Lee Brown or Brandon Haunstrup back to help us.”