St Mirren have confirmed that defender Darren McGregor has suffered his second cruciate ligament injury in two years.
McGregor, who missed much of last season with cruciate ligament damage, was stretchered off during the Buddies' 2-1 defeat by Hibernian.
The 27-year-old missed last season with the same injury to the other knee and will miss the rest of this season.
St Mirren manager Danny Lennon said: "It's a big blow for all concerned - for Darren, the club and the fans."
Before confirming that McGregor had ruptured his cruciate ligament, Lennon praised the defender's "tremendous fightback from injury last season".
"With the backing of our great medical team and his character, I'm sure he will come through it," he said.
Lennon's side sustained their first defeat of the season as Hibs left Paisley with three points.
Leigh Griffiths' opener could have been cancelled out by Paul McGowan, but the St Mirren forward had his penalty saved by Ben Williams.
A second by Griffiths was soon followed by Steven Thompson's strike for the hosts, but an equaliser was not forthcoming.
"I thought the side was unrecognisable in the first half," said Lennon. "When we don't have our passing game, we play deeper and Hibs took full advantage.
"We changed things in the second half and I couldn't have asked for any more except maybe another goal.
"Dougie Imrie and Gary Teale provided lots of crosses and I felt Steven Thompson and Sam Parkin gave them a handful.
"The second half was much more pleasing."
Meanwhile, Lennon admits "finances will dictate" whether St Mirren can retain Kenny McLean, with the midfielder understood to be attracting interest from clubs in England.
"I would certainly like to working with the boy a little bit longer," the manager added. "He is a quality young player."