Sadly, it's not a crossover. Instead, Matt Smith's signed on to star in Patient Zero with Natalie Dormer. And they'll be fighting a pandemic that's resulted in a violent new species.
Patient Zero will be directed by Stefan Ruzowitzky from a script by Mike Le. It takes place when an new rabies strain has resulted in a new species driven by violence. In that backdrop, a human survivor with an unexpected immunity to the disease and the ability to communicate with the new species must find patient zero in order to save his infected wife and family.
While the Deadline article doesn't name Smith's part, from the summary, he's likely to be playing the survivor looking for the cure. No clue who Dormer is playing, whether it's the wife, a scientist he's working with, or someone else entirely.