The former Lazio forward, who has netted four times in 15 games in 2013-14, was injured in training on Thursday and the club have confirmed that his campaign is over
The Czech Republic international has scored four goals in 15 games since joining the club from Lazio in the summer.
He was the most prolific man in the Europa League in 2012-13, netting 10 times, and is Paul Lambert's second-highest scorer this season.
"Villa can confirm that Libor Kozak suffered a broken leg in training," the club wrote on Twitter. "Libor Kozak will undergo surgery [on Friday]."
Paul Lambert's side have struggled in front of goal in 2013-14, with Christian Benteke some way below the form that saw him plunder 23 in his debut season. The Belgian has just five to his name so far, while fellow forwards Gabriel Agbonlahor and Andreas Weimann have three and two, respectively.