29/08/2017 1:34 PM AEST | Updated 29/08/2017 1:34 PM AEST

Bernard Tomic Admits He's 'Not The Smartest Person In The World' After Losing At U.S. Open

'My job's only to play tennis and it's all I know. I'm not going to finish a doctor's degree.'

Julian Finney via Getty Images
Tomic lost in four sets to Gilles Muller. (File Picture)

NEW YORK (Reuters) -- Australian Bernard Tomic admitted he is "not the smartest person in the world" after exiting the U.S. Open in the first round on Monday with a 3-6 6-3 6-4 6-4 defeat to Gilles Muller that could send him tumbling out of the top 150.

Tomic was returning to tournament play for the first time since his first round loss at Wimbledon in July, after which he said he was bored with tennis and had played at 50 percent for much of his career.

The 24-year-old started brightly by taking the first set off the 19th seed on Monday but his lack of match fitness told as, despite frequent treatment from the trainer, he lost the next three to bow out at the first hurdle in a third straight grand slam.

Having already plummeted from 39 to 146 in the rankings since Wimbledon, Tomic now faces the very real prospect of being forced to request a wild card from Tennis Australia for his home grand slam in Melbourne in January.

In typically candid comments afterwards, Tomic said he had his motivation back after his break but still felt "trapped" in the sport he has played fulltime since he was a child, given his lack of other options to fund his lifestyle.

"I mean, it's tough. Everyone has their own work, their own job and it's not like I can go and start real estate or something, restaurants. I've got no idea about that," he told the Australian Associated Press.

"Yes, I can afford to do those things, but I've got no idea. My job's only to play tennis and it's all I know. I'm not going to finish a doctor's degree. I'm not the smartest person in the world."

Tomic's failure to fulfill his huge potential has been a matter of great frustration to his compatriots, and his U.S. Open appearances have featured almost as many controversies as memorable victories.

He bowed out in first round last year after a foul-mouthed rant at a heckler in the crowd, and was given the unflattering nickname of "Tomic the Tank Engine" after his second round capitulation against Andy Roddick in 2012.

Tennis Australia head of performance Wally Masur warned him pre-tournament to be prepared for the grind of the minor tours if he fails to win a match at the U.S. Open.

Tomic, though, reminded journalists he had battled back from a similarly low ranking after double hip surgery in 2014.

"It's no sort of threat for me," he added. "I've been in this position before and I managed to turn it around quickly.

"It's about being healthy the next six months to a year."

(Editing by Peter Rutherford)