"I can't go to the Oscars because I'm going to have a knee operation," said Dench, who's a best-actress nominee for her performance in "Notes On A Scandal."
She presented the movie Monday at the Berlin Film Festival.
"Don't put money on me, because you'll lose it," Dench joked when asked about her chances on Oscar night Feb. 25.
She's up against Kate Winslet, Penelope Cruz, Meryl Streep and the heavily favored Helen Mirren. But whatever happens, she said, "I shall watch and cheer from my bed."
The six-time Oscar nominee won as best supporting actress for playing Queen Elizabeth I in 1998's "Shakespeare in Love."
She stars in "Notes" as a lonely, scheming teacher who discovers a younger colleague, Cate Blanchett, is having an affair with a 15-year-old student.
"I wouldn't want her around," Dench, 72, said of her character at a news conference. "She behaves appallingly."
Her next role is unlikely to be more of the same.
"What I look for is that the next thing I do is completely different," she said. "You try to widen your vision ... the next time I would like to do a film about a circus performer, or something you have to learn about."