The Norwegian forward subsequently left the club's Austrian training camp to return to Stuttgart where a scan revealed that the 28-year-old had damaged cartilage in his right knee, although no decision has yet been taken on what form of treatment he will receive.
"It's certainly a big shame for us, and above all for Moa," said Stuttgart coach Armin Veh. "He's been making a good impression so far in training and now he's unfortunately going to be absent for quite some time. We'll give him all the support he needs to recover and return as soon as possible."
Stuttgart's opening fixture of the 2014/15 Bundesliga campaign takes them to Borussia Mönchengladbach on 24 August.