The 26-year-old, who arrived from West Ham for £2.75million last summer, ruptured cruciate knee ligaments in just his third appearance for the club back in September.
Having undergone surgery and returned to light training it was hoped the former Bristol City forward could make an unlikely return before the end of the campaign, but his manager is targeting a pre-season comeback.
"I do not expect to see Nicky in competitive action for Cardiff City again this season," he told the South Wales Echo.
"There are no miracle cures or quick time frames when it comes to a cruciate injury.
"The aim now is to see Nicky get back his fitness and to be ready to return to full training in pre-season."
Meanwhile, fellow forward Rob Earnshaw has returned to training with his Cardiff team-mates having returned from a brief spell at Maccabi Tel Aviv.