The Spaniard left Old Trafford to rejoin his first club Barca last summer having failed to dislodge mainstays Rio Ferdinand and Nemanja Vidic in the heart of the defence.
The 21-year-old has claimed he was astonished by the eating habits of his former team-mates and said some of the players cannot understand manager Sir Alex Ferguson’s Scottish accent.
He told Sport: “At United there were some incredible things happening. Everyone was allowed to eat what they wanted and one must remember that the English diet is just like people say.
“Every two weeks we had to be checked out on a machine that measured the amount of fat we had in our bodies.
“It would be a surprise that none of the players broke the machine because of the amount of hamburgers and beer they had.”
He added: “The gaffer, as Ferguson is known in Manchester, spoke in English with a Scottish accent but it sounded like Chinese to me.
“But I was not the worst and there are players still there who do not understand him yet.”
Roma manager Eusebio Di Francesco was delighted that his players were able to pounce on Shakhtar Donetsk's mistakes and claim a 1-0 victory on Tuesday.