Jennifer Lawrence is battling pneumonia.

The 'Silver Linings Playbook' star - who is nominated for Best Actress at the Oscars next month - was forced to cancel several planned appearances in Los Angeles this week, including at the Australian Academy of Cinema and Television Arts Awards, because she is extremely ill.

Her co-star Jacki Weaver accepted the award for Best Actress at the event on Saturday, saying: "I am going to accept this award on behalf of Jennifer. She really wishes she could be here, but she is very ill."

Jacki then clarified that the 22-year-old 'The Hunger Games' star - who recently split from her boyfriend of two years Nicholas Hoult - is being treated for the lung infection.

She said: "She has pneumonia."

One guest at the event told the New York Daily News: "Everyone was shell-shocked at what Jacki said. With these ceremonies, when people claim to be ill sometimes there is doubt about how unwell someone really is."

Jennifer, who has had a very busy schedule recently including appearances on the 'Late Show with David Letterman' and hosting duties on 'Saturday Night Live', is said to be eager to attend the Screen Actor's Guild (SAG) Awards Sunday in Los Angeles.

The film's producer, Bruce Cohen, told USMagazine.com that Jennifer is trying to get enough rest so she can attend the event.

He said: "With all her appearances, she hasn't gotten enough bed rest. I haven't spoken to her recently... but I think her plan is to be at the SAGs."