The Bulgaria international has struggled to make an impact for Villa since joining them last summer from Lech Poznan.
The 24-year-old has made 15 appearances in the Barclays Premier League so far, with only six of those being starts, and is yet to score a goal for the club.
Lambert told the Birmingham Mail: "You're looking for more from Aleks.
"But he's got all the attributes there and it's just about trying to get that together and that's why I've put him in and out.
"He's got blistering speed, two great feet and you probably wouldn't know what his strongest foot actually is because of the way he can kick it with both.
"He's taken longer to adjust but you always know that can happen."