Experienced striker Dave Kitson is likely to miss Oxford's FA Cup clash with Charlton at the Kassam Stadium.
The 33-year-old has not started a game since Boxing Day and missed Saturday's win over Wycombe with an ankle problem.
Loanee Nicky Wroe, who scored the winner in the derby on Saturday, will miss out, though, as the midfielder is cup-tied having already represented Preston in this competition.
Midfielder Jon Meades is another who will miss out as he is still only at the start of the comeback trail from an ankle injury.
Meanwhile, Danny Green insists Charlton are out to make the most of their second chance in the FA Cup.
The Addicks were on the brink of a humiliating third-round exit when they fell two goals down to the League Two U's last week.
But a half-time rocket from boss Chris Powell inspired a second-half comeback to secure a 2-2 draw and a replay at the Kassam Stadium.
Winger Green, who set up the late equaliser for Yann Kermorgant, admitted: "I can't repeat some of the stuff the manager said, but he wasn't very happy.
"We knew that , though, everyone did - the players and the fans. You don't want to let yourselves down. You go out there to play for the shirt, play for yourselves and do yourself justice.
"That was the main thing he said and the boys did that in the second half and they did well.
"I used to watch the FA Cup when I was young just like all the boys did.
"You'd love a little run and to play a Manchester United, a Liverpool, a Chelsea or anyone like that. It would be ideal.
"So the away leg is important and we have to go there and beat Oxford."
Saturday's defeat by Middlesbrough has left Charlton outside the Sky Bet Championship relegation zone on goal difference alone.
But Powell, who will be without left-back Rhoys Wiggins after he was red-carded at the Riverside, insists the cup is not a distraction.
"We know our FA Cup record isn't the best in recent years," he said.
"But I'm desperate for us to go on a run as I think that could galvanise everyone at Charlton."