The loosehead made ten appearances in the GUINNESS PRO12 last season for the Warriors as they claimed the title with victory over Munster in the final.
And while the outlook appears bleak for Grant, who was carted off on a stretcher and taken for immediate examination, Cotter is hopeful that the 29-year-old will get the all clear.
"We don't know how he is yet: Ryan's had an X-Ray and we haven't had the results of that," said Cotter.
"We need to wait to be as accurate as we can on Ryan, and we can only wait and see at the moment."
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