The luckless 27-year-old, who has played for his country 29 times, went down with a knee injury on in a Serie A match against Livorno on January 5.
Italy coach Cesare Prandelli said in February he hoped Rossi would be fit to at least travel as part of the squad for Brazil 2014.
Speaking to The New York Times, Rossi said he had turned his attentions to short-term goals rather than looking ahead.
"That (the World Cup) has been my goal from the beginning of the season, but it's not my goal now," Rossi said.
"What I'm thinking about now are the short-term goals. I can't think long-term, even a couple of months. I've got to do the small things first.
"I've got another couple of weeks to rehab."
Rossi spent time at Manchester United – who sent him out on loan to Newcastle and Parma – and Villarreal before moving to Fiorentina in January 2013.
His stint at the La Liga club was particularly painful.
He was out for six months with a right knee injury in October 2011 before missing another 10 after reinjuring the knee in April of the following year.
Another injury to the right knee in January was his latest setback, but Rossi – who is unwilling to set a return date – said he was staying positive.
"It's definitely a pain to fall back again with an injury. You just have to forget about it," he said.
"When I got injured this time it took a couple of days to get past it. When you dwell on something negative it's not going to help you.
"What helps is keeping positive thoughts, keeping your mind fresh and having the right people around you to get past the tough moments.
"After a couple of days I knew that I had come back from injuries before. This injury is not as bad.
"It takes time to heal, but thank God I didn't need surgery. That was a big plus because it takes a lot of patience and hard work to come back."
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