Stefan Wilson was hit from behind by Katherine Legge. The 33-year-old suffered a fracture of the twelfth neck vertebra.
Wilson's brother Justin was killed in a tragic accident during an indycar race in 2015. For a couple of years, the series has introduced so-called "aeroscreens" to protect drivers from similar incidents. The Indy500 takes place in Indianapolis, USA, on Sunday, July 14. The race is expected to be the most competitive in the history of the sport.