The teenager was beaten during a brawl between youths near Holyrood Secondary yesterday afternoon.
Emergency services rushed to the scene and paramedics took a male patient to the nearby Victoria Infirmary. He received treatment for injuries to his face.
Police have launched an investigation into the incident which comes just days after angry parents demanded answers when intruders brazenly walked into the Govanhill school.
The Evening Times revealed a gang of youths entered the school as more than 2000 pupils studied in their classrooms.
It is believed that the incidents are linked and part of a "tit-for-tat" feud between rival teen groups.
One angry parent said: "It's getting worse at Holyrood. First there are intruders in the school, then someone is getting attacked.
"Some people had heard that a pupil had been stabbed - we were frantic."
Previously parents criticised the South Side school - Europe's largest secondary - for not sending out letters about the intruders incident.
Education bosses said a letter would be sent out to all parents today to reassure them.
Glasgow City Council are now looking into a "number of short-term options" to keep pupils safe.
SNP councillor Mhairi Hunter told the Evening Times: "I will be asking questions of both the education department and the school.
"This is obviously extremely worrying.
"Parents expect their children to be safe in school."
Eyewitnesses said there was a large police presence around the school yesterday afternoon.
A Glasgow City Council spokeswoman said: "The school is working with the police to get to the bottom of this matter.
"The safety of our pupils is paramount and we will do everything we can to make sure they can be in their local community without fear of reprisals."
An investigation was launched into the incident at the school on Wednesday, when three youths, said to be former pupils, are believed to have been in the school's reception area.
Concerned parents told how they would be walking their children to and from school after last week's incident. One mother said: "We don't know who these men are, and what they planned on doing."
Councillor Hunter, who represents the Southside Central ward, said she thought security was "very tight" at Holyrood Secondary.
She added: "This is worrying. It is important our schools are safe and secure."
More than 2000 pupils and 130 teachers are based at the city school.
Anyone with any information is asked to contact police on 101.