Born in Beirut in 1957, Mr Midani joined the Old Trafford board in 1987 when United bought the Manchester Giants basketball team, of which he was chairman.
A keen all-round sportsman, he was the Lebanese national junior table tennis champion at the age of 15, and moved to England at the age of 18.
“I was very surprised to hear the news, because 55 is no age,” says United’s honourary president, Martin Edwards. “Amer was a very quiet gentleman who I first met when we bought the Manchester Giants basketball team, with whom he was involved.
“We got to know him when he joined the board and he was always personable and was very well liked around Old Trafford. It’s extremely sad news and he will most certainly be missed by everyone who knew him.”
Sir Alex Ferguson, whose managerial appointment was one of the first major decisions taken by the United board after Mr Midani's arrival, added: "He was very supportive of my appointment and I always appreciated his understanding of my work at Old Trafford."
Everybody at Manchester United football club would like to extend their condolences to Mr Midani’s family.