The Royals kept up their second place form with a 1-0 victory at Stoke City last Saturday, a Dave Kitson penalty separating the two sides.
Blades-Mad are unclear of what side Steve Coppell will field but he did make a statement about his squad selection; "We've had a big physical test against Stoke and we have another big week coming up.
"I'll certainly make some changes but it's an insult to call them fringe players - I'll play a balanced team."
Former Bristol City striker Leroy Lita will be missing for the Royals, the 1M man could be out for a few weeks with an ankle injury.
Possible Royals Line-Up: Marcus Hehnemann, Ivar Ingimarsson, Chris Makin, Nicky Shorey, Ibrahim Sonko, Brynjar Gunnarsson, Bobby Convey, Glen Little, James Harper, Kevin Doyle, Dave Kitson.
The Blades however go into the back of this game following a 1-1 draw with Leeds United last Friday. Frazer Richardson handed the Whites a lead before Steven Kabba pounced to level game.
United boss Neil Warnock has shown that his desire to win the Carling Cup does not match that of winning promotion to the Premier League after fielding under strengthened sides against previous round opponents Boston and Shrewsbury.
The former Huddersfield boss will have trouble fielding the side that beat the Shrews on penalties after most, including highly rated midfielder Stephen Quinn has been sent out on loan.
However we can be sure that once again a less usual line-up will grace the pitch at the Madejski Stadium resting first team players before Cardiff City travel to Bramall Lane next Saturday.
Missing for the Blades will be full-backs Robert Kozluk and David Unsworth. Kozluk came off during the 4-0 away victory over Millwall with an hamstring injury whilst former Everton defender Unsworth will also miss the game with a groin injury.
Skipper Chris Morgan will also sit out the game through suspension after picking up five bookings. Meanwhile Ian Ross has been called back earlier from his loan spell at Boston to play in this rounds fixture, the youngster scored the games only goal in the Round 1 fixture at home to the Pilgrims.
Possible Blades Line-Up: Phil Barnes, Leigh Bromby, Craig Short, Phil Jagielka, Alan Wright, Keith Gillespie, Michael Tonge, Ian Ross, Kyle Nix, Neil Shipperley, Vincent Pericard.
:: Carling Cup Fixtures ::
(all 7:45pm kick-off unless stated)
25.10.05: Aston Villa v Burnley, Blackburn Rovers v Leeds United (8pm), Crystal Palace v Liverpool, Doncaster Rovers v Gillingham, Fulham v West Bromwich Albion, Mansfield Town, Millwall, Reading v Sheffield United (8pm), Sunderland v Arsenal, Wigan Athletic v Bradford City.
26.10.05: Birmingham City v Norwich City, Bolton Wanderers v West Ham United (8pm), Cardiff City v Leicester City, Chelsea v Charlton Athletic, Everton v Middlesbrough (8pm), Grimsby Town v Newcastle United, Manchester United v Barnet (8pm).