He doesn't need surgery yet, but he will have an injection and was advised to sit out the U21s qualifiers.
"He's been to see the specialist and for now we think that he's going to have a special injection and hopefully that will be it," Sven told the City website.
"We are not talking about operating at this moment, so I hope he can start training on Monday, but we are not sure yet.
"He has pain, and has done for a long time, and of course after training and after matches it's gotten worse and worse."
Former England coach, Sven, also praised the understanding of former City boss, Pearce, who gave Johnson his league debut last season.
"I appreciate very much Stuart Pearce," said Sven. "I spoke to him yesterday (Monday) and they agreed that he will not play for the Under-21s.
"That's very good for Michael and it's good for the Under-21s as well because that means he should be ready for the games in November."