The midfielder limped out of last week's 3-1 win at Carlisle with an ankle injury following a heavy challenge and he is yet to recover.
The Irishman is still struggling with swelling so the games over Christmas are a more realistic return date, with David McAllister primed to fill in against Ronnie Moore's side.
The cold weather has restricted the Blades from training over the last couple of days, so they will have to wait until Friday to assess hamstring victims Tony McMahon and Dave Kitson, with boss Danny Wilson not expecting them to be available.
Mark Howard (thigh) and Lescinel Jean-Francois (knee) are back in training, but this clash comes too soon for the duo, who have both been sidelined for lengthy periods of time.
United, who are unbeaten in League One at Bramall Lane this season, will go above Rovers if they can win and will top the table if Doncaster fail to beat Coventry.
"Confidence-wise it will do us the power of good if we can win," Wilson said. "But it's a tough game, Ronnie has done remarkably well."
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