Dr Ihab Anwar, in his late 50s, placed a blanket over his privates and began to rub himself against the passenger during the eight hour journey, the Medical Practitioners Tribunal Service heard.
The woman tried to move away from the Glasgow-based medic, but as she did so the cover slipped down and she caught a glimpse of him, it was said.
Known only as witness A, the shocked woman, originally from Ghana, raised the alarm and alerted the bus driver, the panel heard.
She told the panel she believed the doctor had "faked being asleep" in order to thrust his pelvis towards her. "At the time I thought he was fast asleep until I saw what he did. After what he did I knew it was fake," she said.
The coach stopped at the next service station where Anwar was arrested by Dumfries and Galloway Police. No charges were brought and the Egyptian-born medic continues to 'vehemently deny' the allegations.
But Lee Gledhill, defending, said Anwar was unable to attend the Manchester hearing yesterday. He is currently thought to be in his home country where Mr Gledhill said he was looking after his mother who has breast cancer.
Dr Anwar denies the allegations and that his conduct was 'sexually motivated'.
The doctor, who has been suspended since May 2012, could face being struck off the medical register.
The hearing continues.