The Brazilian missed much of last season after a cruciate ligament injury and said it was very tough.
He revealed that his mother helped him refocus on getting back to full fitness.
"I felt that something very bad had happened [when I did the injury] because I was in terrible pain," said Sandro. "Then I got desperate in that moment. It was the saddest moment of my career.
"It was very hard to deal with this situation because I love football and as I was not able to play, it really hurt me.
"During the early days when my mother was still with me I told her I wanted to quit playing. I only said that because I was in despair. My mother calmed me down by saying that it was going to be alright."
Sandro will be hoping for an injury-free campaign ahead of a home World Cup in Brazil next summer.