Hugh Grant has already played The Doctor
He appeared as the Twelfth Doctor (""The Handsome Doctor") in the 1999 'Children In Need' special 'The Curse Of Fatal Death'
He is noted as being the shortest-lived incarnation of The Doctor, living just long enough to shut off a zectronic energy generator before being hit by excess zectronic energy which immediately killed him
Ironically, he would regenerate into the first female incarnation of The Doctor - Joanna Lumley!