Martin Boyle is out until Christmas after scans revealed the full extent of the injury he picked up against Elgin.
The Hibs winger was desperate to hit the ground running having missed the second half of last season after surgery on the same knee, forced by an injury picked up on international duty with Australia.
It's a significant blow for Easter Road boss Paul Heckingbottom who was desperate to get the best out of the 26-year-old wide man this season.
Boyle was a vital member of Neil Lennon's side that secured the Championship title and finished fourth in their return to the Premiership.
But Heckingbottom could now be forced back into the transfer market after the setback for Boyle.
Hibs face Newcastle on Tuesday night as they step up their preparation ahead of their Premiership opener against St Mirren on Saturday.
