Kehl said treatment plans were still being discussed and a return date had yet to be fixed. Haller joined Dortmund from Ajax on a four-year contract earlier this month.
“Sebastien was operated on last week. We asked for patience at the time. The therapy is currently being discussed. There are various options,” Kehl said ahead of Dortmund’s first-round German Cup tie against 1860 Munich on Friday.
“Sebastien will be out for a few months, but once we can be more precise about that we will communicate it.”
Dortmund had hoped Haller’s physical presence and goals in attack would help them break Bayern Munich‘s decade-long stranglehold on the Bundesliga title.
Kehl said Haller’s absence would be felt but added that the club were preparing for a number of scenarios.
“We have been doing it for a few days. [We are] working on options and ideas, but there is nothing specific at the moment,” Kehl said.
“He will be out for two months and we have a tough schedule until November, but our squad offers options.”