It was announced on Monday morning that the former Lens, Paris Saint-Germain, France, Liverpool, Lyon and Aston Villa manager had passed away at the age of 73.
Houllier is best known for his six-season spell at Anfield and, during his time on Merseyside, the respected Frenchman developed what was already a friendly relationship with Sir Alex Ferguson.
Reacting to the loss, Sir Alex said: “The news has come as a total shock this morning. Gerard Houllier was still a young man at the age of 73.
“Gerard became a really good friend during his time at Liverpool.