The Sunday Mirror claims that Ryan will join the Eleventh Doctor Matt Smith for the show's fifth series in 2010.
A source told the newspaper: "Michelle's been in secret talks with BBC bosses. They are likely to announce her as Doctor Who's new assistant very soon. She is perfect for the role.
"She is good-looking and the right age to star alongside Matt. Everyone agrees they look great together and reckon fans will think they're the perfect team too."
Ryan, 24, is best known for playing EastEnders' Zoe Slater from 2000 to 2005. She also had the lead part in NBC's short-lived Bionic Woman remake, which aired in 2007.