The former Leeds United midfielder picked up his 10th yellow card of the season during their 1-0 defeat to Manchester City on Monday at Villa Park.
The 23-year-old will now miss Villa's clashes against fellow relegation battlers Reading and Queens Park Rangers, which Lambert admits is a massive blow.
"Fabian is playing extremely well. He is playing really, really, really well," Lambert told the club's official website. "His misfortune is going to be someone else's gain. I have a squad and now someone has to step up to the plate and do what he's been doing.
"For the booking itself, you are pressing forward to try and get a goal back and things like that happen. You can't cry about it. You go with the rules and go again.
"I was surprised when I came here and found out how many training days he's done. Fabian has not trained many times since he's been here on successive days. To get him to do that is a big thing, with the injuries he's had. His level of performance in games is extremely high."
Villa travel to Reading on Saturday.