United States international Joe Gyau underwent a second surgery on his left knee last Friday, Borussia Dortmund have confirmed.

Gyau, 22, signed a one-year contract with Dortmund last summer from TSG Hoffenheim, so he could be out of contract by the time he is healthy again. The attacker, who was initially planned for the club's reserve, soon was called up to the first team's match day squad by BVB head coach Jurgen Klopp, and also made his BVB first team debut against Stuttgart last September. He has made just one substitute appearance for Dortmund's senior side but has played well with the reserves.

During a friendly with the U.S. against Ecuador on Oct. 10, Gyau tore his meniscus, and only returned to the BVB reserves ahead of Christmas, coming off the bench in the final three matches of the year.

But Gyau suffered an injury setback during the winter break in Germany, and on Friday underwent knee surgery for the second time in Bad Griesbach, Bavaria, Borussia Dortmund confirmed to ESPN FC.

The attacking midfielder was operated on a cartilage damage in his left knee, and has been ruled out until the end of the season, BVB confirmed to ESPN FC.

Gyau will undergo another examination in eight to 10 weeks, where the exact length of his spell on the sidelines will be determined.