Harry Hunt's co-driver Robbie Durant will undergo surgery in hospital in Plovdiv later today.
The English crew had an incident in SS11 Kantona after they went out of the track.
Hunt, who is leader in the 2WD category, is with a concussion and is not able to remember anything from the situation.
He suffered great pain in the area of the chest, while his co-driver had hurt his back.
The two were sent to the hospital in Sliven for further medical checks and Durant had to be taken to surgeon immediately. That is the reason why he was sent to Plovdiv.
Harry had a 1 point advantage in the 2WD standings to Robert Consani (Renault Megane RS) before the start of Rally Sliven.
Hunt hit trouble at the first full day of the rally as he went out of the road in SS4 Stara Reka 1.
He lost nearly 15 minutes to get back on the track because there was no one around to help the crew.