O'Connor, on loan from Blackburn, has been a virtual ever-present for boss Gary Rowett since arriving at the Pirelli Stadium in the summer, playing in all but two of Albion's league and cup games this season.
But the right-back is nursing a hamstring injury following the league defeat at York on New Year's Day and is a major doubt ahead of the third round tie.
Nathan Stanton, who missed the trip to York through suspension, is likely to deputise at right-back if O'Connor misses out - assuming skipper Zander Diamond recovers from a sickness bug.
"We're hoping Zander will be better by the weekend, which will free up Stanno," said Rowett.
Burton have already beaten Leicester at the King Power Stadium this season, causing an upset in the Capital One Cup with a 4-2 first round win in August.
- Sports & Recreation
- Gary Rowett
- Zander Diamond