The 24-year-old has been nursing a hamstring problem this season, but recently returned to full fitness.
He has, however, not been included in any matchday squads since the turn of the year and has made two just two appearances this term - against Fulham and Stoke City back in December.
Villa have now revealed that Herd will remain out of the first team picture 'until further notice'.
A statement released by the Premier League club read: "The club can confirm that due to personal reasons Chris Herd will be unavailable for selection until further notice.
"There will be no further comment and we request that Chris' privacy be respected."
Herd has also withdrawn from the Australia squad for a friendly date with Ecuador which is due to be staged at Millwall's home ground, The Den, on Wednesday.
Socceroos coach Ange Postecoglou said: "We have been made aware that Chris will be unavailable for selection at club level until further notice as he works through some personal issues and we will respect that and have replaced him in the squad for the Ecuador game."