Jerome Boateng is a doubt to face Slovakia on Sunday

Germany's medical staff are working around-the-clock to get key defender Jerome Boateng fit for Sunday's Euro 2016 last 16 clash against Slovakia.

The Bayern Munich centre-back came off on 76 minutes with a knock to his calf in their 1-0 group stage win over Northern Ireland on Tuesday.

"The hardening is declining, he and the medical staff are working flat out," revealed Germany's assistant coach Marcus Sorg on Thursday.

"We hope that he makes it, but I'm not a prophet. We still have two training sessions, so a lot can happen."

Boateng was more positive when asked about his calf injury, telling German daily Bild he will definitely face Slovakia in Lille.

"The calf is a little hard. I got a stabilising tape on it," said the 27-year-old. "Our medical department does an excellent job. I'll definitely be able to play on Sunday."

Boateng made a crucial goal-line clearance against Ukraine in the opening group game

Boateng has been a standout performer at Euro 2016, especially with an eye-catching goal-line clearance against Ukraine in Germany's 2-0 opening win.

Alongside Mats Hummels at the heart of Germany's defence, Boateng's performances in Brazil two years ago were a key factor in their World Cup triumph. He has won 62 caps for his country.