Montgomery sustained a knee injury in Saturday's 1-1 draw with Millwall and is waiting to learn the full extent of damage to his cartilage and ligaments.
The Blades will also be without defender Rob Kozluk, who sits out the second of a three-game suspension.
Lee Williamson, however, returns from his ban and could step in for Montgomery, while Johnny Ertl provides manager Micky Adams with an alternative option.
Striker Jamie Ward will not be included as he recently became a father for the first time.
Defender Nyron Nosworthy is hoping to make his first appearance since sustaining an ankle injury on New Year's Day after returning as an unused substitute against Millwall.
Adams is chasing his first win as Blades boss after nine games in charge.
Source: PA
Source: PA