The former France international hung up the boots earlier this year.
Umtiti admits his injury problems at Barca left him feeling isolated and lonely.
Speaking with La Gazzetta dello Sport, Umtiti recalled: "In Barcelona, I felt very alone. I didn't want to talk to anyone. Meanwhile, injuries were constantly affecting me, and I was playing very little.
"If you're not emotionally well, your body can't perform at its best, and that affects your performance. It's crucial that footballers receive the necessary support because we're often thrown into a world that's enormous and difficult to manage.
"It's important to have the courage to admit when you're not feeling well, to say it out loud."
Umtiti also recalled breaking down in tears when greeted by Lecce fans as he prepared to sign for the Serie A club in 2022.
"I'm not a very talkative person; my heart speaks louder than my mouth. Perhaps those tears came straight from my heart. I was coming from a very difficult period, where I felt that people didn't understand me.
"I needed genuine love, and I found it from the very first moment in Lecce. Director (Pantaleo) Corvino told me I would fall in love with the people and the city. I wasn't so sure; I came from Barcelona, and to be honest, I didn't know what to expect. But he was right; a very strong bond was formed."