The Premier League champions posted a message on their official Facebook page saying: "Happy 28th Birthday Ashley Young! Wish Ash a Happy Birthday and good luck for the new season here..."
While a number of fans sent over their birthday wishes, there were a few that used the platform to express their dislike towards the former Aston Villa player.
One user wrote, "sell him for his birthday", while another posted, "HB! You need to find another team big boy".
Young signed for the Red Devils in 2011.