The 19-year-old tumbled from the roof terrace in the early hours of the morning at the five-star Blythswood Square hotel. The hotel has confirmed that he was one of their employees.
A foot long spike from nearby metal railings was lying on West George Street where the man landed.
Blythswood Square was closed to traffic for several hours and a section of West George Street remains cordoned off.
Inspector Kenny Darroch said: "There was a small group who appeared to have been at a party in the penthouse and the man has fallen.
"He is now at Glasgow Royal Infirmary. He's alive but he has horrendous injuries."
Several police officers remain at the scene this morning, keeping watch over the cordoned off area.
Inspector Darroch said: "We're preserving it while we take photographs, do a bit of analysis and take statements."
A single suited officer from the CID arrived at 8:30am, carrying two brief cases.
A police officer at the scene who asked not to be named said: "There is no investigation - we're not looking for anyone - but there's obviously protocol to follow."
The £1,500-per-night penthouse is described as "magnificent" on the Blythswood Square website.
It has a rooftop terrace, private bar and dining room and boasts views over the city which "will quite literally take your breath away", the website said.
Guests are treated to a bottle of Dom Perignon 2003, Epernay Champagne, on arrival and a well-stocked complimentary mini bar is available.
Managing Director at Blythswood Square, Hans Rissmann, confirmed that there had been an incident at the hotel around 5am this morning during which a 19-year-old man fell from the roof onto West George Street.
He said: "The young man is currently in hospital and contact has been made with his relatives. Everyone's thoughts are with them at this time.
"The man is an employee of the hotel and was a guest of a guest who was staying in the Penthouse at the time and is a former employee.
"It is believed that the incident was an accident and that there is no suggestion of anything suspicious. The hotel is providing every co-operation to the authorities.
"This is a very distressing time for everyone associated with the hotel. A full inquiry will be undertaken in order to understand the circumstances surrounding this accident."
A spokeswoman for Police Scotland said: "Around 5am a report was received of a man having fallen from the roof of a building in the centre of Glasgow.
"We're still trying to piece together the circumstances."
She added: "Road closures will remain in place for quite some time."