Barnsley keeper faces lengthy absence
The German is set to have surgery on the problem later this week, and the Tykes' physio Richard Kay knows it will be a long road back for the 29-year-old.
He told the club's official website: "It looks as though Heinz has done some very serious damage to his anterior cruciate ligament. There's also some damage to his lateral meniscus.
"The MRI scan was a little cloudy because of all the blood in the area so we're unsure as to whether Heinz has ruptured his cruciate or not.
"Whether it's a total rupture or a partial tear will determine what the surgeon does this week and could potentially effect how long he's out for.
"Heinz will definitely be out for between six and nine months. That's the best and worse case scenario and a lot of it depends on any complications with his surgery and how well he comes through the rehab programme.
"To be honest we'll probably know more after the weekend but it will be a long-term injury."