Billie Piper may not appear in every episode of the second series of Doctor Who on BBC One, according to reports.
Billie Piper stars as Rose Tyler
Piper, who plays the Doctor's assistant Rose, will return for the new series but it is not confirmed for how many episodes, said a BBC spokeswoman.
"With regard to how many episodes she will be in, we are currently story-lining series two," she said.
Christopher Eccleston has already said he will not return as the Doctor - David Tennant will become the timelord.
The return of Doctor Who has been a huge success for the BBC - both critically and with audiences.
But the loss of Eccleston was a blow for the corporation looking to build on the success of the first series.
The show has been developed by Russell T Davies, writer of Queer As Folk and The Second Coming, who is a lifelong Doctor Who fan.
The BBC spokeswoman said plans for the second series had not been finalised.
"It has not been confirmed how many episodes she will be in," she said.
"We are waiting to see the storylines and scripts."
Filming on a new 13-part adventure and Christmas special will start at BBC Wales later in 2005.