The actor told What's On TV that the episode may feature another development in the relationship between Matthew and Mary (Michelle Dockery).
"He might be moving on a little bit," he teased. "But there's a lot of things up in the air that need to be resolved."
However, Stevens refused to say too much about what is coming up in the episode.
"Downton has a very big Christmas tree, I can tell you that much," he said. "I can't tell you much else but it's a bit Christmassy."
Meanwhile, ITV has revealed that the two-hour special will be set in 1919 and feature a Christmas party at the Abbey.
However, Bates's arrest will be a hot topic of conversation, Mary will consider her future with Sir Richard Carlisle and the Dowager Countess will be worried about Rosamund's new beau Lord Hepworth (Nigel Havers).
The Downton Abbey special will air at 9pm on ITV1 on Christmas Day.
> Downton Abbey's Dan Stevens to host Have I Got News For You