Williams left the Iron to join the Royals on a free transfer this summer and will start at left-back for Brian McDermott's men as they look to start their Championship season with a win.
Winger Jimmy Kebe was a revelation after Christmas last season but is a doubt to play with a groin problem, while Noel Hunt may have to wait to make his first-team return.
Hunt missed most of last season with a knee injury and is now struggling with an ankle knock - but fellow Republic of Ireland international Shane Long is fine after a head injury.
Grzegorz Rasiak is back from a rib injury but Julian Kelly (groin), Ivar Ingimarsson (hamstring) and Chris Armstrong (knee) remain out.
