The three players sat out Saturday's drawn home fixture with Walsall after picking up injuries during the win at Leyton Orient the previous Wednesday.
Parkinson remains hopeful that none of the injuries are anything too severe but he admits it would be pointless to take risks on any of the threesome at this stage.
Parkinson said: "It is a blow not to have them with us for Tuesday but we have to make sure we bring them back in only when they are right.
"Dava (Andrew Davies) and Hans (James Hanson) are just minor we believe, while we are keeping our fingers crossed it is hopefully the same with Fil (Filipe Morais).
"We will go to Swindon in a confident frame of mind, especially after our recent away performances, and prepared for how they might set-up against us."