The man was walking along Onslow Road, near the railway bridge at Drumry Railway Station, at about 05:30 on New Year's Day when he was attacked by a group of people.
He was taken to the Queen Elizabeth University Hospital where he is being treated in the high-dependency unit.
Police said there was no apparent motive.
Officers have been reviewing CCTV from the area and discovered that there were a number of people in the area at the time.
Det Insp Grant MacLeod said: "This appears to be a totally random attack, with no apparent motive, leaving a man seriously injured.
"Our inquires have revealed that despite it being fairly early in the morning, there were various people in the vicinity at the time of the attack and I am appealing to these people to get in touch.
"It's possible you can provide information on the suspects which would assist our investigation in locating those responsible for this violent attack."

Mkhitaryan, 27, signed for £26m from Borussia Dortmund but was left out of the side repeatedly until recently.
But in his third successive start, he struck his first United goal in their Europa League win over Zorya Luhansk.
"He worked really hard physically, tactically and we know the talent is there," said Mourinho, 53.
Mkhitaryan was a substitute in United's opening-day win at Bournemouth but was hauled off at half-time in his first league start at Manchester City in September and did not feature again in the Premier League until late November.
During the Armenian's absence, Mourinho said the midfielder needed time to adapt to the English game and called on the 2015-16 Bundesliga players' player of the year to "do more".
"He has a strong mentality," Mourinho added. "He was very determined to fight against his difficult adaptation, and he's doing that in the best way.
"He fought to improve tactically, he fought to improve physically, and now he is playing good in the Premier League, good in the Europa League and the EFL Cup, and now evolving a bit more happiness for him, so I'm very pleased."
Mkhitaryan's excellent run and finish put United ahead in Ukraine and Zlatan Ibrahimovic's late strike sent them into Monday's last-32 draw as Group A runners-up behind Fenerbahce.
Mourinho rested several players including goalkeeper David De Gea and his stand-in Sergio Romero was visibly surprised when a firecracker landed in his six-yard box during the first half.
"Maybe Uefa is not happy and maybe Uefa now takes some money from Zorya, which I think Zorya doesn't deserve," added Mourinho.
A 40-year-old man has serious injuries after being stabbed by a gang in a "random" attack in Clydebank.
[NEXT_CONCEPT]
Manchester United boss Jose Mourinho has praised Henrikh Mkhitaryan's fighting qualities in adapting to his summer move to Old Trafford.