Police said the man was walking with two friends in Fernhill, Ruth- erglen, when a thug ran up and stabbed him.
His two pals ran off unharmed before the alarm was raised.
The injured man was taken to Glasgow's Victoria Infirmary where he is being treated for his injuries.
His condition there is described as "critical but stable".
The incident occurred in Shieldaig Drive, near its junction with Barrisdale Way in the South Lanarkshire town at about 8.40pm on Wednesday.
Police are appealing for witnesses to the attack to come forward with information.
Detective Chief Inspector Pat Campbell, who is leading the investigation, said: "This appears to be a totally unprovoked attack on this young man as he was out with his male friends.
"Police are currently carrying out inquiries in the local area in an effort to gather more information on this attack.
"I would urge anyone who witnessed this incident, or who may have information that may assist police inquiries, to come forward to us as a matter of urgency."
Police have issued a description of the suspect.
He is aged between 20 and 30, around 6ft tall and slim. He was wearing a grey hooded top.
Anyone with information should contact Rutherglen Police Office on 0141 532 5200 or Crimestoppers can be contacted on 0800 555 111, where anonymity can be maintained.