Ospreys coach Steve Tandy expects new lock De Kock Steenkamp to be a long-term injury absentee with an Achilles injury.
The 27-year-old South African, who has joined from the Stormers, has yet to play a competitive game for Ospreys.
"We've got to speak to the surgeons, the people who know the time frames... but yes, I'd assume [months out] with an Achilles," Tandy said.
"I feel sorry for him... he's done one fitness test and broke down."
Steenkamp first revealed the injury on social media, tweeting: "Not the ideal start to the season, again... Thing can only go up from here #tornachilles."
The 6ft 6in lock, who hopes to qualify for Wales on residency in 2017, accompanied his tweet with a picture showing himself bandaged and on crutches.
The Welsh region are unbeaten in the Pro12 ahead of their revamped European Rugby Champions Cup campaign, which kicks off against Treviso on Sunday, 19 October.