The American striker has joined the Bluebirds on a season-long loan from Premier League side Fulham, and is likely to feature at some point.
Defender Gabor Gyepes is cup-tied following his appearance for Northampton in the opening round of the competition, while Mark Kennedy is rated doubtful after he limped out of Saturday's 2-2 draw against Norwich with a groin injury.
Kennedy told the South Wales Echo: "It's just a little thing I've been carrying since the first game of the season. I'm sure there's not a player in the dressing room who doesn't start a game without a niggle.
"It just got too painful in the end and I'd have thought I'd be iffy for Tuesday's game."
Manager Dave Jones could also be without midfielder Gavin Rae and defenders Kevin McNaughton and Tony Capaldi, who are all battling knee injuries.
MK Dons manager Roberto Di Matteo will be forced into at least one change.
The Dons were superb in a 3-1 win at much-fancied Huddersfield on Saturday but will be without Shaun Cummings.
The on-loan Chelsea youngster played on the left of midfield at the Galpharm Stadium but is barred from playing in the competition by the Premier League giants so Jemal Johnson could start in his place as Florian Sturm (groin) is out.
Defenders Luke Howell (thigh) and Danny Swailes (Achilles) remain sidelined so the back four will remain unchanged.
Captain Keith Andrews was again not in the 16 for the Terriers trip as he seeks a move away from the club before next week's transfer deadline and will not be involved at Ninian Park.