Bundesliga top scorer injured in training
In a statement on their website, the club said Ibisevic, who has scored 18 goals this season, may have ruptured a cruciate ligament during close-season training in Spain.
The injury is a major blow to the surprise league leaders with the Bundesliga resuming in just over two weeks.
Ibisevic had to come off after being injured in the final minutes of Hoffenheim's 2-0 defeat by Hamburg, the club said.
"A first examination has raised the suspicion of an anterior right cruciate ligament rupture," the club said. "He is expected to return home and undergo a detailed examination in Heidelberg."
Hoffenheim, in their first Bundesliga season, have taken the league by storm topping the standings at the halfway mark with Bayern Munich second on goal difference.
Ibisevic, 24, largely unknown at the start of the season having joined Hoffenheim when they were in the second division, had been outstanding so far netting 18 goals in 17 league matches to help turn the newcomers into title contenders.