Borussia Dortmund midfielder Axel Witsel will miss Saturday's game at Union Berlin after tearing a thigh muscle, the Bundesliga leaders said on Thursday.

"Yesterday evening the club received a diagnosis on the injury suffered by Axel Witsel. Unfortunately Axel has torn a muscle in the adductor area," Dortmund said in a statement.

The club didn't confirm how long the 30-year-old Belgian international would be out of action.

Dortmund will be hoping the Belgian will be fit in time for their first Champions League group-stage match against Barcelona on September 17.

Witsel joined Dortmund from China's Tianjin Quanjian last year after impressing at the World Cup in Russia.

He has since been pivotal for his side, missing just one Bundesliga game since the start of last season.

Witsel is likely to be replaced by Julian Brandt, who shone from the bench in the 3-1 win over Cologne a week ago.