Manager Remi Garde has been left decidedly short of attacking options for Saturday's visit of Norwich City.
The 26-year-old Czech, who previously suffered a career-threatening leg break in January 2014, had only recently broken back into the first-team fold after impressing Garde in training, making three straight Premier League starts last month.
However, he was forced off in the second half of the 0-0 draw at Midlands rivals West Bromwich Albion two weeks ago after taking a knock to his ankle and has since missed the 4-0 FA Cup fourth round defeat to Manchester City and Tuesday night’s 2-0 loss at West Ham United, respectively.
Garde initially hoped that the formerly out-of-favour front man would make a swift recovery, but he has now revealed that the problem is worse than first feared.
Asked to give an injury update at his pre-match press conference ahead of Saturday’s visit of Norwich City, the Villa boss said: "Unfortunately, Libor will be out for a few weeks now because he's got a little fracture on the ankle.
"He will be out for three or four weeks probably.”
Kozak was replaced by Rudy Gestede during the West Brom derby, but the Benin international later had to be substituted himself after pulling his hamstring with 10 minutes left of the match.
The towering forward has also missed the past two matches, and while he is expected to be back sooner than Kozak, the Norwich game has come too soon for him to make a comeback.
Ashley Westwood could be available, however, after missing Tuesday night’s loss with an ankle injury, with Garde adding: "I could rely on Ashley Westwood. I am not 100 percent sure yet. But he could be back within the group.
"Rudy will be back earlier than Libor, for sure, but he won't be available for this weekend.”
Meanwhile, Jordan Ayew was shown an early red card on Tuesday night for elbowing West Ham left-back Aaron Creswell in the face, meaning he will now serve a three-match ban.
It leaves Villa with only one out-and-out striker available for Saturday in Gabby Agbonlahor, who is on an 11-month goal drought and was expected to leave the club in the recent transfer window after seeing just one minute of action in Garde’s first 14 matches in charge.
However, the long-serving forward made his first start since 2 November against West Ham after recovering from niggling calf and back injuries, and his manager was pleased with his performance given the tough circumstances.
“We have many injured players - and a suspended player as well,” Garde said at his press conference. "Gabby is back in the group. What he showed in the West Ham game was interesting.
“His attitude was very positive for the team. In his position, when you are playing with ten men it is the worst position because you run everywhere.
“He showed a good example of what I’m asking him to do as an experienced player. I was pleased with what he did.”