Leigh Banks, 36, was wounded during a quarrel with the bus worker over valuables he said were missing from his wallet which he had forgotten on the bus.
The tourist was seriously wounded in his left torso. A passerby helped send him to Mahachai 1 Hospital where he received emergency treatment.
Before the incident, Mr Banks and his wife and another 20 passengers travelled by the bus from the southern province of Surat Thani to Bangkok.
Other passengers got off the bus along the way and only the couple was left on the bus. The bus stopped at a petrol station in Samut Sakhon, where the driver told them to wait for a new bus take them to Bangkok.
After taking their two bicycles from the bus and the bus departed Mr Banks realised that he had left his wallet and passport on the bus, and he called the bus driver to return.
The bus came back to the petrol station and Mr Banks alleges that his wallet had been rifled through and his valuables were missing. He asked a bus worker and the two men quarrelled. The staff worker stabbed the tourist before fleeing by the same bus.
His wife asked for help and a Thai woman, a passerby identified as Sumalee Yisunkaew, drove to a petrol station and called an ambulance for them and also called the police.
The police are searching for the bus, which was initially found to be operating illegally, that is without proper licensing to transport tourists.