Caterham said in a statement that Kobayashi "remains part of the team".
Lotterer, 32, is a three-time Le Mans winner and previously tested for the Jaguar F1 squad in 2001 and '02.
Caterham believe they will benefit from his experience, particularly in mixed conditions that are often typical to Spa, and that his feedback "will contribute to improve the performance of the car".
Lotterer said he was delighted by the unexpected chance to make his first Grand Prix appearance.
"I'm ready for this challenge and I cannot wait to jump in the car and make the most out of the weekend ahead," he commented.
"I will need to get settled and used to the car quickly, as the team has worked on a number of updates and we will need to have as much time as possible out on track to optimise the car's performance.
"I really enjoy racing at the legendary circuit of Spa-Francorchamps, it's one of my favourite tracks and it's very close to where I grew up, so this makes the weekend even more special and one to remember."
Although Lotterer has not driven F1 machinery for more than a decade, he does have recent single-seater experience in Japan's Super Formula. He won the series title in 2011 and lies second in this year's championship behind former Williams F1 driver Kazuki Nakajima.
The German has also raced alongside his new Formula One boss Christijan Albers, with the pair competing in the 2009 Le Mans 24 Hours in sister Audi cars run by former F1 team chief Collin Kolles, now advisor to Caterham's new investors.
Caterham have yet to break into the points since entering F1 racing in 2010. They lie 11th in this year's standings, with Marcus Ericsson's 11th place in Monaco their best result of the season to date.