Borussia Dortmund manager Jurgen Klopp has revealed that defender Manuel Friedrich is on trial at the club following the long-term injury to Neven Subotic.
Serbia international Subotic is likely to be out of action until next summer with a cruciate ligament injury and Klopp hopes that Friedrich can prove his fitness levels in the coming days.
The former Germany international has been a free agent since his departure from Bayer Leverkusen in the summer after playing at the BayArena for six years.
"Manuel Friedrich has experience, he holds quality," Klopp told the club's official website. "Now it's about seeing how much fitness he has.
"At the end of the trial, we will have to come up with the best decision for the club.
"Given the injury to Neven Subotic, we had to quickly sort things out."
Klopp also revealed that, when Friedrich was promoted to Mainz's first team, he decided to retire from playing himself.
He added: "Friedrich is a very adaptive person, a very kind and intelligent lad. He was a factor in me retiring from my career as a player.
"When he joined us at FSV Mainz 05, I immediately considered retirement."