Houlier died in France just a day after undergoing heart surgery.
The former France manager who also managed Paris Saint Germain, Olympique Lyon, Lens and Aston Villa suffered a number of heart problems during his managerial career.
Ferguson and Houlier’s paths crossed several times in opposing dugouts during their respective spells as managers of England’s two most glamorous clubs.
Houlier was in charge of Liverpool between 1998 and 2004, leading the Reds to five major trophies, including a famous treble of FA Cup, League Cup and UEFA Cup in the 2000/2001 season.
"The news has come as a total shock this morning,” Ferguson, who retired as a manger in 2013 after leading Manchester United to their 20th league title, told the Red Devils’ official website after hearing of Houlier’s death.
"Gerard Houlier was still a young man at the age of 73. Gerard became a really good friend during his time at Liverpool.
"We remained great friends after he left and he was always a great ally to have. He had fantastic football knowledge which he gained during his extensive and varied career.
"When we saw each other at UEFA meetings or other events, we would often enjoy a chat, he was always great company and I will miss him dearly. He was a true gentleman.
"It is a sad day for the football world and my thoughts are with his family at this desperately sad time."
