Pompey will be without Anton Walkes for their crucial trips to Plymouth and Bradford.
The on-loan Tottenham star – who has featured at right-back and in midfield for the Blues – limped off at the end of Saturday’s draw with Rochdale.
He has since been diagnosed with a hamstring injury, ruling him out of the games at Home Park this weekend and Valley Parade next Tuesday.
But assistant manager Joe Gallen is confident that Pompey have enough fit bodies to cope with his absence.
He said: “We were hoping that it was going to be cramp, but that’s not the case and there is a hamstring strain.
“It’s always tough to put a time on those injuries, although he certainly won’t be fit for Saturday’s game or the one next Tuesday.
"I’m sure it’s frustrating for Anton because he’d been playing really well and is a very flexible player."
“We’re disappointed by that of course, but there are enough good players here to be able to fill in for us.
“Stuart O’Keefe’s back and as soon as he came on at Rochdale, it seemed to have a galvanising effect on the team and crowd.
“Connor Ronan’s done nothing wrong during his time with us, while Dion Donohue could move into that position as well.
“I’m sure it’s frustrating for Anton because he’d been playing really well and is a very flexible player, so hopefully he’ll be back soon.”
Christian Oxlade-Chamberlain is also set for a spell on the sidelines after suffering a broken leg in training on Monday.
Gallen said: “It was a freak situation really because there was nobody around him at the time.
“He was just taking a shot during a five-a-side game and his foot got stuck in the ground. He heard a crack and you could tell from his facial expression there was something wrong.
“X-rays have confirmed a fracture and it’s bad timing for him, but he’ll certainly be back and we wish him well with his recovery.”