Forster is on loan at the club from Newcastle but is not eligible for the cup competition.
Defender Steve Elliott has been sidelined by a thigh strain so far this term but was on the bench for the 1-0 win over Huddersfield on Saturday so could come into contention for a start.
Summer signing Dominic Blizzard will again have to settle for a place on the bench as he tries to improve his fitness following his move from Stockport.
Manager Paul Trollope has no other fitness concerns as he looks for a cup upset at the home of the Championship leaders.
Cardiff boss Dave Jones looks set to have an almost full squad to choose from.
The Bluebirds have full-backs Tony Capaldi and Mark Kennedy available once again after they both missed Sunday's Severnside derby against Bristol City.
Capaldi returns after a one-match suspension while Kennedy is back in the fold after a thigh injury.
There may also be a first start for Kelvin Etuhu who made his debut as a substitute at the weekend following his season-long loan move from Manchester City
Stephen McPhail will also be hoping to be involved after he returned to the bench against the Robins following a hamstring injury.
Kevin McNaughton (ankle) remains four or five weeks away from full fitness while striker Ross McCormack will be sidelined for between six to eight weeks with a hamstring injury.
Sporting Life