Police are appealing for information

Constable Martin Devlin, 35, had undergone emergency surgery at Glasgow's Southern General Hospital following the attack.

The 21-year-old robbery victim was said to be in a "serious" condition in the same hospital following the incident in the Ibrox area of Glasgow.

The plain clothes officer had been taking part in an operation to target robberies in the area.

He was wearing protective body armour, but is believed to have been stabbed near the shoulder.

The other man was stabbed in the torso.

Strathclyde Police are hunting four men, who were all wearing white jackets with black stripes on the sleeves.

'Full attention'

Sergeant Allan Agnew said: "This is a serious incident because a member of the public has been seriously injured.

"It is quite unusual for a police officer to be stabbed and the incident is receiving our full attention.

"Closed circuit tapes will be reviewed to see if we can get a better identification of the persons concerned."

The incident happened close to The Stadium pub opposite Ibrox Underground station shortly after 2200 BST on Friday.

The incident took place near the Ibrox Underground station

Police have been carrying out an investigation into a spate of robberies in the Ibrox area.

They sprang into action after spotting the 21-year-old man being attacked.

A police spokesperson said that the robber stabbed both PC Devlin and the other man.

The assault on the 21-year-old is being treated as attempted murder, while the attack on PC Devlin is being treated as a serious assault.

The attacker and the rest of his gang fled following the incident.

A large area of Copland Road, close to Rangers' Ibrox Stadium, was cordoned off by police officers.

Police appeal

One was seen removing a large wine bottle from the entrance to the station and broken glass from outside the pub.

Officers remained at the scene until 0100 BST.

PC Devlin is married with four young children. He has 11 years police service and is stationed at Govan police office.