Former World No. 1 Rafael Nadal has cast fresh doubt over his participation at the Rio Olympics, saying he is yet to recover from a wrist injury.

The 14-time Grand Slam winner has been sidelined since withdrawing from the French Open in May.

"I will not be at the best level in any of the categories," Nadal told reporters after arriving in Brazil. "I have not competed for two months and I have not trained a lot."

"I will train a few days here to see what I can do and then decide what is best, to be more positive for me and the team.

Nadal won gold at the Beijing 2008 Games but missed the London Olympics four years later because of a knee problem.

The 30-year-old, who is expected to be Spain's flag-bearer at the opening ceremony on Friday, will compete in the singles and also the mixed doubles with French Open winner Garbine Muguruza.