The club revealed the 20-year-old will undergo surgery on his right knee after suffering the injury playing for their under-21 side against Stoke on Wednesday.
The problem rules Gardner out for almost the entire season with him expected to be back in late April at the earliest.
Villa boss Paul Lambert told the club's website: "It's a blow and it's definitely a blow for the lad but he's very positive and he'll get great attention all the way through his rehab."
Gardner suffered a similar problem in his other knee in 2009.
Source: PA
Source: PA