Russian Maria Paseka, who beat Simone Biles on vault at the 2015 World Championships, is not certain to compete in the Olympics due to a back injury, according to Russian news agency TASS.
Biles is considered a clear favorite for four gold medals — not done by a female gymnast since Romanian Ecaterina Szabo in 1984 — and could win five golds — never done by an American woman or a female gymnast.
Biles captured gold medals at the last two World Championships in the team event, all-around, balance beam and floor exercise.