Winger Yeates, unavailable for the FA Cup defeat at Bolton after sealing a permanent move for an undisclosed fee last week, could start as midfielder Lee Williamson has been ruled out with a recurrence of a hamstring problem.
But Blackwell has a shortage of central defenders at his disposal following last week's sale of Matt Kilgallon to Sunderland, with his replacement Marcel Seip sustaining a hamstring injury of his own in the warm-up prior to the Bolton match.
Jonathan Fortune stepped up to partner Chris Morgan in the absence of on-loan Plymouth defender Seip, who has been ruled out for six weeks.
Reading are set to be unchanged from the side which beat Burnley.
The Royals pulled off another FA Cup shock at the weekend when they knocked out Premier League side Burnley at the Madejski Stadium with top scorer Gylfi Sigurdsson notching his ninth of the season.
The Icelandic midfielder was a doubt to face the Clarets after missing the defeat at Nottingham Forest the previous week with a foot injury but after lasting 90 minutes against Burnley will again feature.
Brian McDermott will once again be without Noel Hunt, Chris Armstrong and Julian Kelly.
Hunt and Armstrong continue to recover from knee surgery while full-back Kelly is out with a shoulder injury.
The trip to Bramall Lane will see Reading fans reunited with James Harper, who made nearly 350 appearances for the Royals before joining United on loan in September.
Sporting Life