The British filmmaker, who is reassembling the cast for a 10-minute film for Comic Relief, is still in talks to bring back Thompson’s character Karen.
While stars including Liam Neeson, Hugh Grant and Keira Knightley have already been confirmed to star, it seems that Thompson is yet to sign on the dotted line.
“Oddly, we're not quite sure [if she'll be in it],” he told Victoria Derbyshire.
“It's all been done in a great rush and I think not but I'm now thinking again.”
Thompson starred opposite the late Alan Rickman in the 2003 film, playing a heartbroken wife who discovers her husband has feelings for another woman.
Neeson and his on-screen son Thomas Brodie-Sangster were spotted shooting scenes for their segment in London earlier this week.
“Amazingly, nobody said no," said Curtis "Liam flew over yesterday from America and is going back to America tomorrow. There is a lot of affection for the film."
Curtis’ other half and script editor Emma Freud said that she had to do a lot of work on his draft.
“I’ve never been more useful as a script editor than I was on this because the first draft he did on this was so bad that I told him we absolutely shouldn’t do this and we should abort the plan,” she said.
“And he rewrote it and rewrote it and it’s quite good now but it’s very much for Red Nose Day. We’ve tried to hook it into that at every point and that felt a bit like a crowbar at the beginning but it’s working quite nicely now.”