Newcastle manager Steve Bruce is hopeful they will have some players back for Tuesday's trip to Sheffield United, but urged caution with captain Jamaal Lascelles.
The Magpies skipper made his first appearance since November 21 when he started the 2-0 loss at Arsenal last weekend.
Lascelles had not played in six weeks after he tested positive for coronavirus and struggled to regain fitness following his battle with the virus.
While the centre-back started at the Emirates on Saturday, he had to be withdrawn at half-time and may not be ready to feature against the Blades, who are bottom and without a Premier League win this season.
"We hope we can get a few bodies back," Bruce said.
"It was let's see how Jamaal goes and that is what we are all stabbing in the dark about. It is not a groin strain or a hamstring, it is the after effects of what he has had.
"We played it by ear to see how much he could continue and to be fair to the lad you could see he was out on his feet at half-time. We brought a certain freshness in and it will be good that he has got 45 minutes under his belt."
Callum Wilson and Jonjo Shelvey were not involved due to a precaution while defenders Fabian Schar and Federico Fernandez were left at home as Newcastle named only seven substitutes for the third-round tie.
One of them was 18-year-old Elliot Anderson, who made an impression from the bench and almost helped the Magpies grab a winner at the death, but his deflected shot into the path of Andy Carroll could not be converted.
Bruce added: "As soon as Elliot comes onto the pitch, he accepts the ball and receives it and has got that lovely look where he never looks rushed.
"Everything is effortless to him and easy. We hope he has a big future. He will remember his debut – he could have scored in the last minute and what a wonderful debut that would have been.
"I am very pleased with his progress and he is one we hope can do us a good turn over the rest of the season."
Martin Dubravka was impressive for Newcastle in the capital on what was his first outing of the campaign after a heel injury.
Karl Darlow has deputised well in the Slovakian's absence, but Bruce conceded he has some thinking to do ahead of the Bramall Lane clash.
"I am delighted with the goalkeeping situation," he added.
"We have got two quality goalkeepers and Martin again has reminded what a good goalkeeper he is and Karl has been very, very good all season. I have one of them awful ones where let's hope I pick the right one."
The pressure on Bruce's opposite number Chris Wilder eased on Saturday after Sheffield United grabbed a first win of the season at the 19th attempt.
It was only against third tier opposition in Bristol Rovers though and the Blades are aware they are already being cut adrift at the bottom of the table with just two points from 17 league games.
"If you are managing in the Premier League, you are under pressure it doesn't matter who you are," Bruce insisted.
"They are a very decent side, they have had an awful run and there is no disputing that, but they still have the same players which this time last year got them to sixth or wherever they were.
"It can be the Premier League but if we play like we did over the last week, we will give ourselves an outstanding chance."
