Captain Vlaar has been out since early November with a calf injury while England rookie Delph dislocated his shoulder in October.
Vlaar only returned to training this week while Delph had been expected to be out for most of the Christmas period, but Villa boss Paul Lambert revealed both could possibly make surprise returns at The Hawthorns.
"Ron is coming back, he's been training this week, as has Fabian, which is good," said the Scot.
"We'll train tomorrow and see how the lads are and how they feel.
"We'll gauge it by that but they've been training, Ron this week and Fabian for the last two weeks.
"Hopefully it goes okay tomorrow and we can judge it then
We'll talk to the lads."
Lambert would appreciate the pair returning in light of his current injury struggles.
Vlaar's defensive colleagues Philippe Senderos and Nathan Baker are some way off regaining fitness
Joe Cole, who suffered a recent hamstring problem, has been joined by midfield mainstay Ashley Westwood on the sidelines after he suffered medial ligament damage ruling him out for around a month, while Tom Cleverley is struggling with a bruised foot.
Lambert added: "We're having a spate of ups and downs with injuries at the moment.
"We've had another injury added to the list, with Westy being out which is a blow because he's been playing really well.
"Tom Cleverley is another one who is a cause for concern but we'll have to wait and see, because he's got another two days before the match."
Recent derby clashes with the Baggies have been entertaining affairs and Lambert expects Saturday's Barclays Premier League battle to be no different.
"Anywhere you go, derby matches are massive for supporters," he said.
"They always want to get one over on their workmate or whoever it is
"The derbies between Villa and West Brom that I've been involved in have always been really good games with lots of goals in them and I don't think this one will be any different.
"The atmosphere will be really good and we're in a bit of form so we'll go there trying to win."
Source : PA