Caddis, who has missed the Robins' last four matches with an ankle injury, is still at least a fortnight away from a return to full fitness and will not feature for Town on Saturday.
Joe Devera is likely to fill in at right-back once more, while Aden Flint is pushing for a recall in the middle of defence.
Winger Luke Rooney and on-loan striker Jonathan Tehoue are both available to manager Paolo Di Canio after being cup-tied for the Johnstone's Paint Trophy final defeat to Chesterfield at Wembley last weekend.
Left-back Jay McEveley made his Swindon debut under the famous arch and is set to continue against Rovers, while John Bostock will be hoping for his full debut after joining on loan from Tottenham.
However, forward Paul Benson is a doubt for the Robins with a minor knock sustained during the loss against the Spireites.
Bristol Rovers' injury problems are all but over.
Gary Sawyer returned to the starting line-up in the 1-0 defeat at Aldershot in midweek following a hamstring problem, while fellow defender Aaron Downes is also available having shrugged off a knee cartilage knock.
Competition for places in the Rovers rearguard will be intense ahead of the trip to the County Ground, with on-loan Tom Parkes also back in contention after illness.
Goalkeeper Michael Poke is pushing for a comeback following his spell on the sidelines because of an ankle problem, while Wayne Brown is also back in training after his ankle injury.
However, the midfielder's target is to return before the end of the season and he is unlikely to feature against the Robins.
Adam Virgo remains a long-term casualty with a knee ligament injury.