Head coach Chris Ramsey confirmed both men had suffered injuries during the 4-1 victory over West Brom, and they will not feature as the strugglers go in search of back-to-back wins.
Vargas opened the scoring at The Hawthorns but was substituted after half an hour with a knee problem, while Clint Hill replaced Yun with eight minutes to play.
"Yun won't play [against Villa], he's concussed," said Ramsey. "You've got to take precautions with head injuries, so he won't be in the squad.
"And Eduardo has damaged his knee. We're going to a have to wait for the swelling to go down, before we can send him for a scan to assess the extent of the damage.
"But I'm not one to moan about injuries, we've got a 25-man squad for a reason and you won't hear me moaning about who is and who isn't available."
