Union Berlin and Bayer Leverkusen have expressed their sympathy to the family of former coach Sascha Lewandowski, who has died at the age of 44.

Having been promoted from a role with the club's youth team, Lewandowski coached Leverkusen's senior side jointly with Sami Hyypia from April 2012 to May 2013 and served as interim head coach when the former Liverpool defender left the club in April 2014.

He took over at Union Berlin in September last year but stepped down in March on the advice of doctors after being diagnosed with acute fatigue syndrome, a severe form of burnout that led to heart problems.

"It is hard to imagine for us that Sascha is dead," Leverkusen sporting director Rudi Voller said in a statement.

"He was a great man who brought all his strength and passion in his work... Sascha did a fantastic job. Our deepest sympathy goes to his [family].

"We are all shocked and deeply concerned," Leverkusen chief executive Michael Schade added.

"Our thoughts are now with his partner and his family. Sascha Lewandowski was a wonderful person who has left their mark in Leverkusen.

"His name is closely linked to the sporting success of our club in recent years. It's terrible that he is now no longer among us. We had all hoped to see him again in the summer on a bench."

Union Berlin president Dirk Zingler said: "We are deeply shocked and incredibly sad.

"Our sincere condolences and our deepest sympathy to the family and relatives of Sascha Lewandowski."

Lewandowski began his coaching career with Vfl Bochum's reserve team.