The 41-year-old man had left a boxing event at about 22:00 on Saturday with two companions when they were attacked.
The man was taken to Forth Valley Royal Hospital where he reported to be in a "stable" condition in the intensive care unit. His companions were given medical attention for minor injuries.
In a second incident, a 25-year-old man was robbed by men who may have been at the boxing event at the Albert Halls.
Appealing for information on the serious assault, Det Sgt Colin Moffat said: "We have descriptions of two of the men who carried out this attack.
"One is described as being white, in his mid 20s, muscular build, black spiky hair with both arms covered by sleeve tattoos. He was wearing a cream or white T-shirt.
"The second man is described as white, again in his mid 20s, slim build, short dark hair and was wearing a blue coloured blazer.
"Anyone who may have been in the area of The Back Walk is asked to call us at Stirling on 101 if they saw or witnessed this assault and can help identify those responsible."
In the later incident, police said the 25-year-old was approached by three other men in Murray Place at about 22:50 on Saturday. They stole money from their victim, leaving him "badly shaken".
It is thought the attackers may have been at the boxing event nearby.
A boxing fan has been seriously injured in an attack in Stirling.