Oxford have Tony Capaldi, Paul McLaren and Tom Craddock missing.
Defender Capaldi will have to wait further for his debut after being sidelined with a back injury which caused him to miss the season's opener against Rotherham.
McLaren and Craddock were also absent from the 1-0 defeat at the Millers and have been ruled out of the first-round tie due to knee injuries.
Chris Wilder could still name an unchanged side from the weekend, in which six new signings made their debuts for the Us.
Oxford will be hoping to repeat their round one efforts of last season, when they demolished Bristol Rovers 6-1 in their first Carling Cup match for four years.
Cardiff have eight players away on international duty.
The list of absentees includes Don Cowie, Kevin McNaughton, Kenny Miller and Robert Earnshaw, meaning manager Malky Mackay will have to call on his youngsters for the clash.
The absence of strikers Miller and Earnshaw gives new-boy Rudy Gestede a chance for a first start for the Bluebirds, following an impressive substitute appearance at the weekend.
The Frenchman came on for his debut against West Ham in the 67th minute and made his presence felt before helping set up Miller's late winner at Upton Park.
Stephen McPhail, who is now back in full training, is also hoping to be involved in the tie having recovered from a virus.