The game goes ahead despite heavy rain but Reds go into the match without defender Claude Davis and striker Billy Clarke.
The pair are only considered fit enough for the bench after only returning to training on Thursday.
Davis injured his knee at Stevenage last week and was replaced by Joe Walsh at half-time. Walsh starts for the first time in six games in place of Davis.
Clarke misses his third game in a row due to the hamstring injury suffered in the FA Cup win against Chelmsford City.
In his absence Reds stick with the 4-5-1 formation which they used at Stevenage as Dannie Bulman retains his place at the base of the midfield.
Sheffield United make two changes to the side which drew 0-0 with Tranmere last weekend, Kevin McDonald and Dave Kitson coming in for Chris Porter and Marcus Williams.
Crawley (4-5-1): P Jones; Hunt, Connolly, Walsh, Sadler; Adams, Akpan, Bulman, Simpson, M Jones; Alexander. Subs: Kuipers, Davis, Torres, Clifford, Clarke, Akinde, Ajose.
Sheff Utd (4-4-2): Long; McMahon, Maguire, Collins, Hill; Blackman, Doyle, McDonald, Flynn; Miller, Kitson. Subs: Westlake, McAllister, Cofie, Ironside, McFadzean, Williams, Coyne.