Pompey will still be without some of their key players against Gillingham this weekend.
But skipper Brett Pitman and winger Gareth Evans are closest to returning out of all the injured players.
The duo have been sidelined since limping off with hamstring problems in a League One defeat at Southend a fortnight ago.
Saturday’s game comes too soon for the pair, although they are now both on the road back to full fitness.
Blues boss Kenny Jackett said: “They won’t be ready for this weekend, but they’ll be the first two to return of the players that are currently out injured.
“We won’t be able to use them against Gillingham and we’ll have to see whether they’ll be ready for the following game.
"It’s not something that you can really rush and so we’ll be keeping a close eye on how they progress."
“They’re coming back from hamstring injuries and it’s hard to assess, but they were both running outside for the first time today (Monday).
“It’s not something that you can really rush and so we’ll be keeping a close eye on how they progress.
“There won’t be anyone back this Saturday that wouldn’t have been available at the weekend and Nathan Thompson’s still got two games of his suspension to go.
“Stuart O’Keefe’s a very positive person and will try everything in his power to get fit. We’ve conservatively targeted April, although he’ll always try to shave a week or two off!”
Pompey had a rare weekend off after Saturday’s scheduled match at Bradford fell victim to the wintry conditions.
Jackett said: “You could see it building up and at least nobody had to travel up because it was one of the longest trips on the fixture list.
“It was pretty inevitable when you saw the number of games that were called off, but the snow’s cleared up and hopefully we can have a good run between now and the end of the season.”