Schmelzer out of Dortmund's Champions League quarter-final
Borussia Dortmund defender Marcel Schmelzer hurdles a challenge by Zenit St Petersburg defender Alexander Anyukov during the Champions League last 16 second-leg in Dortmund, western Germany on March 19, 2014 - by John MacDougall
"The diagnosis is a torn muscle in the pelvis area and it'll be four weeks before he can train again," said Dortmund coach Jurgen Klopp on Thursday.
The 26-year-old suffered the injury in the later stages of Dortmund's 2-1 defeat at home to Zenit St Petersburg on Wednesday in the last 16 of the Champions League.
Dortmund progressed to the quarter-finals with a 5-4 win on aggregate having won the first-leg in Russia 4-2 three weeks ago.
The draw for the last eight will be made on Friday, but Schmelzer will be missing for both legs of the quarter-final clash which will take place on April 1/2 and April 8/9.
Schmelzer's injury is the latest in a string of ailments to befall Dortmund, who are already without centre-back Neven Subotic and winger Jakub Blaszczykowski, who are both out with long-term knee injuries.
Dortmund are hoping Germany winger Marco Reus will return for Saturday's Bundesliga match against Hanover 96 after missing the last few weeks with a leg injury.
"I can't say yet. He has recently trained well and it was all positive, but I must wait to see how the injury reacts," said Klopp when asked if Reus will play.
"If he's fit, he'll play."