Warnock's injury crisis deepened when defender Matthew Connolly sustained an ankle problem in training this week.
"Callum is having an operation on Monday and should be out until pre-season," Warnock told a news conference ahead of Sunday's home league match against Chelsea.
"It's a big blow. On the same day Connolly was just coming back training as well and he dislocated his ankle."
Cardiff's weekend clash against Chelsea and next Wednesday's trip to Manchester City could have a major bearing on the Welsh club's hopes of avoiding relegation, as they are currently two points adrift of the safety zone.
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Warnock could not have done much to prevent Paterson's injury but he was left frustrated by Iceland manager Erik Hamren, who opted to play Gunnarsson in both of their Euro 2020 qualifiers against Andorra and France.
Gunnarsson has been hampered with injuries this season and Warnock had hoped 29-year-old midfielder would be afforded some rest during the international games.
"Originally I was told they weren't going to play Aron on the plastic pitch for the first game (against Andorra); he played for over an hour," Warnock added.
"And then he plays against France for 93 minutes. I know it's a new manager (Hamren took charge after last year's World Cup), you want to do well, but when you're 3-0 down with 80 minutes gone, surely you can substitute a player.
"We've been treating him, he's not played two games and all of a sudden we've got Chelsea and Man City in the space of three days. I just thought it was pure selfishness and I'm so disappointed in Iceland for doing that."
(Reporting by Hardik Vyas in Bengaluru, editing by Pritha Sarkar)
