The Athletic reported that the Argentine international has injured his anterior cruciate ligament (ACL) and will be sidelined for an "extended" spell.
"Aston Villa can confirm Emi Buendia has suffered a significant knee ligament injury," Villa said in a statement.
"The midfielder sustained the damage during training yesterday and has subsequently undergone a scan. Buendia will now be under review ahead of a further consultation with a knee specialist."
Buendia was a key player for Villa last season, making 38 appearances as they underwent a remarkable turnaround under coach Unai Emery, finishing seventh and securing qualification for the Europa Conference League.
The Premier League season begins on Friday and Villa travel to Newcastle United for their first game on Saturday.