The Portuguese flyer came in to United as an unknown 20-year-old when Sir Alex Ferguson was in charge.
Bebe has now revealed that leaving United was the best moment of his life.
"It wasn’t that (I didn’t believe in myself), I just know what life is like and I think anyone would have the same thought as me," Bebe told Goal in 2018.
"If you are playing in the third or fourth division in Portugal and suddenly one of the best teams in the world calls you, I think anyone would think ‘can this actually be true?'
"Every day I called my agent to ask him to get me out. It was a bad time. When you do not play, even if you are at a great club, then you are not happy, so why continue?
"I remember that I was going for a United game with the youth team, and my agent called me and told me I had been sold to Benfica. It was the best moment of my life."
"I can’t regret something that has given me so much food, that changed my life and the life of my family. United gave me everything," Bebe continued.
"That’s where everything started for me.
"I could have a car, a house, I could buy things that I couldn’t have bought before. I could help my family and friends in things they couldn’t do... I do not regret anything. It was a very good decision from me and my agent.
"If I had the mentality then that I have today, I would definitely still be there. I would be in a team like that. But I had a different childhood from the others, and the attitudes and thoughts I had were different.
"That did not help me at all, not that I regret it. But now I would tell my younger self to train more, to be more concentrated, to be more professional."