"It is a great chance for us to get through to the fifth round," he said. "This club hasn't been there for a long time now. We will be treating it with respect."
With their approaching Uefa Cup commitments, coupled with the league, O'Neill is expected to make changes, with Brad Guzan in goal instead of first-choice Brad Friedel. But Barry promised that they would not be underestimating their opponents.
"We have got a busy schedule in February with two games a week all the way through but [Doncaster] need to be treated with respect. We saw when we played them away they created a lot of chances. We have to have a good team there to beat them."
Barry is the only player still at the club to have featured in the 2000 Cup final against Chelsea, who ended up winning 1-0, which gives him added impetus to see the club progress to the business end of the competition.
"That was a great day out for myself and my family and the club," he said. "It is certainly something you want to get back to again."
In the absence of Martin Laursen, O'Neill had given the captaincy to Barry. Considering he was stripped of the role this season for his intention to leave for Liverpool, it shows that the relationship between the two men has improved significantly.
"The relationship is very good," Barry said. "It can go through your head what others have done to get away from a club and it was just not the reputation I would have wanted. I've got too much respect for the club, and for the manager."