"Gul has been diagnosed with three stress fractures of his spine by a South African expert in Cape Town. According to him he will not be able to play cricket for one year," said a PCB statement on Wednesday.
The 20-year-old seamer suffered the injury in Pakistan's historic series against India in April after he took 5-31 to anchor team's win in the Lahore Test.
"Gul will be returning to Pakistan on Wednesday after spending a week in Cape Town undergoing diagnosis and treatment from one of the world's leading sports medical clinics for a recurring back pain," the statement said.
"He will be reassessed in six months as the fracture has to heal first, before his re-habitation starts."
Gul burst onto the scene with a brilliant performance in the ICC Junior World Cup held in New Zealand in 2000 and made his One-day debut in Sharjah last year.
He has played five Tests taking 25 wickets and his 15 One-day Internationals fetched him 19 wickets.
Pakistan's newly inducted coach Bob Woolmer had said Gul would have to alter his action modelled after star Australian paceman Glenn McGrath to avoid injuries.
Pakistan's chief selector Wasim Bari described Gul's injury as a setback for the team.
"With a hectic season ahead and Pakistan going to Australia later this year, Gul's injury is a set back," said Bari.