The right-back (Achilles) and right winger (hamstring) have yet to resume training.
Buckley's late goal at The Amex knocked Newcastle out in the fourth round last year.
Boss Gus Poyet has vowed to field the strongest side available to him in the quest for a repeat.
Gus Poyet: "Apart from when we were in League One and convinced the only thing that mattered was getting up, in the rest of the years we were fair with the cups. We played the best team on the day.
"This one is tricky because it is on TV against a Premiership team, so you cannot be silly and not play your best team. We are going to play with the best we have.
"If Bruno is fit he will play. I'm not going to say it is maybe better to leave him until the week after. It is the same with Bucker but the problem is they are both not training today."