The Black Cats have had to battle a number of defensive issues in recent weeks, but were boosted by the return to training of a number of key players towards the end of last week.
Lynden Gooch and Conor McLaughlin are the two most likely to return to face Portsmouth.
Gooch failed a late fitness test on Saturday after struggling with a calf problem against Swindon Town days earlier. However, a scan showed there was no permanent muscle damage and so the Black Cats are confident he will be able to return soon.
McLaughlin has responded well to an injection following hernia surgery and is expected to return either at Fratton Park or Wembley.
Bailey Wright and Tom Flanagan are closing on a return but Tuesday's game could come too soon.
"Lynden was still feeling his calf on Saturday [so we'll see]," Jamie McAllister said.
"We obviously had a few back in training on Friday so we'll just have to see how everyone is doing."
The televised game at Fratton Park starts a crucial run of games for the Black Cats, who face a number of sides also in promotion contention.
Sunderland are in confident mood following a sequence of seven games unbeaten, and McAllister said it was credit to the squad that they had built a platform for the run-in despite the injury issues.
"It's credit to the lads, how they've trained and how they've recovered," he said.
"We have to keep that going.
"When we start to get those injuries clearing we'll be even stronger and give the manager a lot of selection headaches."
Sunderland were seven points adrift of Portsmouth when their unbeaten run began last month, but that has become a five-point advantage ahead of Tuesday's game.
Portsmouth boss Kenny Jackett is under increasing pressure from the fanbase after their poor form culminated in a 4-1 defeat to Northampton Town on Saturday afternoon.
Sunderland are braced for a reaction from their opponents and McAllister said that result underlined why no fixture in League One can be seen as straightforward.
He says his squad simply have to focus on themselves ahead of the run-in when they will face a number of promotion challenges.
"I don't think it's any more important than any other,” he said.
"It's three points at the end of the day and we've just got to focus on what we do well.
"We'll look at their threats but we will go for three points whoever we play.
"You look at Peterborough and Portsmouth's results on Saturday, they've struggled against teams down the bottom.
"We had a tough game against Crewe ourselves.
"It shows that you can't underestimate anyone in this league, you have to be at it every game.
"Our confidence is high but there's still a few things we can improve on, so we've got to keep at that.
"The application of the group has been first class.
"We've got to keep building."