New York (AFP) — Rafael Nadal admitted Monday that he wasn't sure when he will return to action after Frances Tiafoe condemned him to his earliest US Open exit since 2016.

Four-time US champion Nadal, bidding for a 23rd Grand Slam title, lost 6-4, 4-6, 6-4, 6-3 in the last-16 to 26th-ranked Tiafoe.

The American's free-swinging performance conjured up 18 aces and 49 winners which flew past a sluggish Nadal on Arthur Ashe Stadium.

For Australian and French Open champion Nadal, it was a first Grand Slam loss of 2022 after an abdominal strain forced him to forfeit his Wimbledon semi-final.

The defeat ended a run of 16 successive Slams where the Spaniard had made at least the quarter-finals.

"I need to go back. I need to fix things. I don't know when I going to come back," Nadal told a press conference.

"I am going to try to be ready mentally. When I feel that I will be ready to compete again, I will be there."

Nadal has endured a rollercoaster year.

His two Slam titles have taken him one clear of Novak Djokovic but his physical frailties have also returned to haunt him.

Nadal suffered a stress fracture of the ribs in March before requiring daily pain-killing injections in his left foot to see him through to a 14th French Open title in June.

Then his bid for a third Wimbledon crown was shattered by an abdominal injury.

Nadal is due to become a father for the first time in the coming weeks, which will factor heavily into his future on-court plans.

"Now I have to go home, I have more important things than tennis to attend to," he said.