Mane suffered the setback in his first senior season.
He told the Mirror: "I still remember. I was the young player in the team, but I felt responsible. The day the team was relegated, I was crying like never I did before. The people around the club, I felt so bad for them.
"I felt bad maybe because that day I missed two chances, and if maybe I scored we would stay up. So I felt it was my fault, and I was crying all day. Then the day after, the club offered me a five-year deal!
"I wanted to stay with the club until we came back up again. Then Salzburg came and they paid £4m, and it was the club who said: 'sorry but you have to go!'. I didn't want to leave."