On the contrary, it has been confirmed (in "The Night of the Doctor" & "The Day of the Doctor") that there was an incarnation between the Eighth Doctor (played by Paul McGann) & the Ninth (played by Christopher Eccleston). This was the "War Doctor" (played by John Hurt). This incarnation didn't use the name "Doctor", though others did use it of him, which is why he's not included in the numbering.
In "The Time of the Doctor", it was also confirmed -- in dialogue between the Eleventh Doctor & Clara Oswald -- that there are no other unknown past incarnations of the Doctor. Thus, the faces seen in "The Brain of Morbius", for example, can't have been past incarnations of the Doctor.