The 30-year-old man was working at the Dalmarnock building site when five youths with their faces covered and wearing black clothing robbed him at knife-point.
As the guard chased them, one of the gang hit him over the head with a brick.
Detective Constable Ewan Gilmour, of London Road Police Office, said: "We are carrying out extensive inquiries and checking CCTV to trace those responsible for this assault and robbery. I would like to appeal to anyone who was around the Belvidere Avenue area on Wednesday night and saw a group of youths hanging around the Commonwealth Games site, or anyone hanging around to contact me."
The guard heard a noise outside his cabin shortly before 7pm on Wednesday. He went outside to investigate and was confronted by five youths who threatened him with a knife.
Three of the thugs went in to search the cabin while two others held the guard outside.
The gang took a backpack containing a Sony laptop, a wallet containing bank cards and two mobile phones.
As they ran off on to Belvedere Road, the guard chased them but one of the suspects hit him on the head with a large brick.
The guard then made his way to a nearby house and called police. He was later taken to Glasgow Royal Infirmary where he was treated and discharged.
The suspects are all described as white, Scottish and aged between 14 and 20.
Two of the gang were wearing balaclavas that had silver edging around the eyes and mouth. The other suspects wore scarves to cover their faces. They are all described as wearing black clothing.
Anyone with information that could help the inquiry can contact London Road Police Office on 0141 532 4600.