Rafael Nadal is still being troubled by his wrist injury, insisting it is "not perfect" after losing the bronze medal match to Kei Nishikori at the Rio Olympics.

The 14-time grand slam champion suffered a 6-2 6-7 (1-7) 6-3 defeat to Nishikori on Sunday, finishing the 2016 Games without a singles medal.

Nadal, Spain's flag bearer, made his return from injury in Rio, having been sidelined since the French Open due to his left wrist.

In worrying news ahead of the US Open, the 30-year-old said the injury was still a problem.

"The wrist is not perfect. It bothers me when I hit the forehand. The serve, the backhand - nothing else bothers me," Nadal said.

"The truth is, when I hit the forehand, I feel it bothering me a little bit, but without a doubt it's been a positive week in all aspects. I've played for many hours and the wrist at least didn't get worse."

Nadal will leave Brazil with a gold, after teaming up with Marc Lopez to win the men's doubles.

Asked whether his performances showed him he could compete at the top level, Nadal said he already knew as much.

"No. I was ready to win Roland Garros when I had to go. I won in Monte Carlo, won in Barcelona, played the semi-finals in Indian Wells.

"I was close to beating Novak [Djokovic] in Rome - I was playing at a high level when I had to stop, but when you stop in the middle of the season, it's always very tough.

"The other players don't stop, keep their rhythm and you have to find your rhythm back again. I believe that this week will help me to move forward."

As for Nishikori, who won his first Olympic medal, the Japanese star was thrilled, saying: "I'm very happy to win, to get a medal today.

"Even though it's third place it means a lot to me, especially beating Rafa today. I knew that if I played good and solid tennis I would have a chance to get a medal.

"So I was playing for my country and this is something different than other tournaments. I was enjoying it a lot and I'm sure this experience will help my confidence and my future."