Although Ibrahimovic was confirmed to leave last month and Preston had already announced the signing of Harrop on a free transfer last week, the club issued a statement of the four players that have left.
Ibrahimovic said farewell to his United followers on Instagram with just six words: “I came. I said. I conquered.”
The club have already removed Ibrahimovic and Harrop’s profiles from the first-team section on the official website, which leaves the number nine shirt available for a potential summer arrival.
United youngsters had already confirmed Diedrick-Roberts’ summer departure in as they wished him well with the Instagram posts, as the 18-year-old was surpassed by United’s other youngsters.
Makela was impacted by growth-related injuries which left him with just one academy start in successive seasons, before his final campaign at the club.
He made his Under-23 debut at Leicester in April but had already started a youth loan with League One Bury as a result of a lack of game time.