Ninth Doctor 2 (The Tomorrow Windows)

A possible ninth incarnation of the Doctor was seen by the Eighth Doctor in the Tomorrow Window. The figure shrugged and gave the Eighth Doctor an apologetic, lopsided smile. He had unruly, curly hair and resembled a scruffy student. (PROSE: The Tomorrow Windows)

Behind the scenes
The description of this incarnation matches that of, who was a rumored actor for the Ninth Doctor in 2003 before the reveal of Christopher Eccleston.