Heskey out for four weeks
The former England forward, who retired from international football after the World Cup, had been in good form, scoring three goals in six games since the arrival of new manager Gerard Houllier.
"Heskey tore the medial meniscus in his right knee yesterday (Wednesday) in training with no other player involved in the incident," read a statement on the club website.
"The injury will require an operation and the powerful forward faces between three to four weeks out of action."
Heskey is now likely to miss Villa's next five Premier League games and is a doubt for their League Cup quarter final against local rivals Birmingham City on December 1.