Inverness summer signing Owain Tudur Jones is to have surgery on Tuesday after picking up a cartilage problem.
And manager Terry Butcher admits that the Wales midfielder faces up to eight weeks on the sidelines.
"Owain sustained a blocked knee against Rangers and it has been diagnosed as requiring a cartilage operation," Butcher told his club website.
"It's a massive blow to the lad and to the club as we're looking at a six to eight week lay-off."
Jones, who arrived was released from his contract by Norwich City this summer and was recalled to his national squad, went off injured after 65 minutes during Saturday's 2-0 defeat at Caledonian Stadium.
Caley Thistle say their new recruit, who signed a one-year contract with the Scottish Premier League club, is stunned by the news that he requires surgery.
"But Owain is determined and he'll start his rehab right away," said Butcher, who expects Jones to return to action in October.
Jones joins Lee Cox, Billy McKay, Josh Meekings, Kenny Gillet and David Proctor on the casualty list at Caledonian Stadium.
"That means we have six players out, which is a dreadful start to the season in injury terms," added Butcher, whose side next face Aberdeen this weekend.
"None of the five who missed the Rangers game will be back within a fortnight, so the squad is fairly stretched.
"Add on Ross Tokely's suspension and we're looking at seven being out for Pittodrie, which is a challenge."