On-loan Ipswich striker Ellington, yet to score in three appearances for the Iron, has been out with a calf strain, while midfielder Walker has been on the mend from ankle ligament damage.
Ellington was due to face Carlisle on Saturday, in a match that was postponed due to a waterlogged pitch, while Iron boss Brian Laws had suggested Walker would miss out against the Cumbrians but could be in contention for the squad against the the Blades.
Karl Hawley will continue up front, but centre-half David Mirfin remains sidelined with a knee ligament injury. The Blades, who moved top of the table with a 2-0 win at Crawley on Saturday, are favourites but will be fearful as the Iron are their bogey team.
Of the 10 meetings between the two teams this millennium, the Iron have won five while the Blades have come out on top only once - a 2-1 victory last year, which saw Scunthorpe battle for an hour with 10 men after Sam Togwell was sent off.