Hoffman, 30, twisted his ankle at training on Sunday and missed the Jets' Asian Champions League victory over Indonesian team Persija Jakarta on Tuesday.

Despite initial hopes the injury wasn't too serious, a Sydney specialist has revealed Hoffman suffered a dislocated tendon in his ankle and he'll need to undergo surgery.

It expected the injury will sideline Hoffman for five months, with surgery on Monday.

"This is a huge blow for us but I'm really just disappointed for him to be missing so much football," Jets coach Ernie Merrick said.

"It was a fairly innocuous sort of incident and we were hopeful it would only be something minor, unfortunately it was confirmed that Jason will be out for an extended period."

Youngster Joe Champness has been named as Hoffman's replacement in the Jets' 18-man squad for their playoff with Champions League title holders Kashima Antlers.

The clash with the Japanese powerhouse will be played in Kashima on Tuesday.

Australian Associated Press