Sterling, 31, was the subject of questions at Tuchel's press conference on Friday after a turbulent period on and off the pitch.
The former England international was charged with dangerous driving and possession of nitrous oxide in August, while he remains without a club following a short spell at Feyenoord.
Tuchel was Chelsea manager when the club signed Sterling from Manchester City in 2022 and said he had personally pushed for the transfer.
“I fought to get the transfer through, and he never managed to show the importance he normally had. It was a big step for him at that point,” Tuchel said.
The England manager then turned to Sterling's current circumstances, making clear that he remains concerned about someone he remembers as a committed family man.
“It's sad to see someone struggle, because he was a devoted father to his children and a family man, a nice person to be around,” Tuchel said.
“It just seems that he is going through a difficult period.”
Sterling left Chelsea after a spell in which he struggled to establish the influence he had previously enjoyed at Manchester City. He subsequently spent time on loan at Arsenal before leaving Stamford Bridge.
The winger joined Feyenoord on a short-term deal last season but was unable to score or provide an assist in eight appearances for the Dutch club.
Tuchel, who worked with Sterling at Chelsea before being dismissed early in the 2022/23 season, also suggested that circumstances can sometimes develop into a difficult cycle.
“I'm not sure how much of it is his own fault. Sometimes you just enter a strange spiral in life, a downward spiral.”
Despite Sterling's current situation, Tuchel said he continues to believe the player can recover his career.
“My thoughts are of course with him, and you always believe that he can turn it around. I wish him all the best.”
Sterling has won four Premier League titles and earned 82 England caps during a career that has also taken him to Liverpool, Manchester City, Chelsea, Arsenal and Feyenoord.
For now, however, he remains without a club as he looks for the next stage of his career.