Steyn aggravated a shoulder problem before lunch on the second day of the first Test against Australia.
Steyn, who first hurt his shoulder late last year, aggravated the problem before lunch on the second day of the first Test against Australia in Perth as his series came to a premature end.
The 33-year-old right-armer had just bowled the fourth ball in his 13th over when he clutched at the shoulder and left the field.
Scans at a local hospital revealed a fracture in his right shoulder and he will return to South Africa for possible surgery at the conclusion of the Test.
Team doctor Mohammed Moosajee said Steyn, who is just four Test wickets shy of Shaun Pollock's South African record, was likely to be sidelined for at least six months.
"Today while he was bowling he felt something thud or pop," Moosajee said.
"He will return home and see an orthopaedic surgeon in Cape Town and a decision will be made on what the best method of treatment will be.
"I assume in all likelihood that he will need surgery.
"The estimated return date we will have to wait and see, the literature says six months, but we don't know."
Moosajee said it was unclear what caused the original injury, which he said was a very rare stress reaction.
He said Steyn had experienced some discomfort in the shoulder during a warm-up match in Adelaide, but scans had revealed no problems.
Moosajee said Steyn was extremely disappointed and admitted the bowler's future was "up in the air".
"Time will tell, but only when healing has occurred will we be able to make a call on whether he can come back and play," he said.
"Knowing the kind of person that he is, he will make every effort to get back onto the park. He has been through adversity before and knowing Dale he will come back much stronger."
Fellow paceman Morne Morkel is expected to be available for selection for the second Test in Hobart, starting on November 12.