Novak Djokovic spent the recent US Open with his own private hyperbaric chamber parked up next door to Flushing Meadows.

The world No 1, who retired from his fourth round match with a shoulder injury, had an oxygen chamber stationed on the back of a lorry outside the gates but within the Corona Park area where the tournament is situated.

Tournament officials have confirmed the highly unusual measures he took, which illustrate just how important Djokovic views the treatment to his overall well-being.

Novak Djokovic brought his own private hyperbaric chamber to the recent US Open

According to witnesses an area was closed off to accommodate a trailer that was split into three compartments and positioned throughout the event for his exclusive use, adjacent to the New York Hall of Science, around 300 metres from the Arthur Ashe Stadium.

Djokovic is currently nursing the left shoulder problem which caused him to abruptly quit when trailing by two sets against Switzerland's Stan Wawrinka.

The 32-year-old Serb has long been an advocate of the hyperbaric chamber which, it should be said, is legal under WADA regulations. The first record of him employing one was in 2011 and since then their use - facilitating the breathing of 100 per cent oxygen to improve performance and speed recovery from injury - has become more widespread across different sports.

The egg-shaped chambers are used by athletes to improve performance and speed recovery

It is, however, decidedly uncommon for someone to bring one in to have at their own disposal. He is also said to have brought in the lorry at other events in North America this year, such as Indian Wells and Cincinnati.

A spokesperson from the US Tennis Association, which runs the US Open, confirmed to Sportsmail that his tractor trailer was standing in a car park by the Hall of Science, one of the museums located in the park around Flushing Meadows.

Djokovic is currently undergoing more treatment on the injury and it is the subject of conjecture when he will return as the tour heads to Asia.

Djokovic retired from his fourth round match at Flushing Meadows with a shoulder injury

He initially targeted the Japan Open at the end of this month and tweeted last week that he was 'actively working on my recovery so I can be ready for the Asian swing. My health is always top priority and as soon as I'm ready, I'll be back.'

A spokesperson for the player, who on Monday overtook Jimmy Connors by spending his 269th week as world No 1, did not respond to inquiries.

Djokovic is the main absentee from this year's Laver Cup, beginning on Friday between the six-man teams of Europe and the Rest of the World in Geneva as it alternates between one side of the Atlantic and the other.

The Serb made a low-key exit after having to concede the match to Stanislas Wawrinka

The players, including recently crowned US Open champion Rafael Nadal, congregated on Wednesday by the shores of Lake Geneva before heading back to the city's Palexpo arena for practice.

The Lawn Tennis Association have confirmed that Britain's biggest women-only tournament, the Nature Valley Classic, has had its prize money slashed to £200,000 as part of a revamp of the grass court season which will see a new 'Premier' level event take place in Berlin.

The move to downgrade the heavily loss-making event, revealed by Sportsmail last month, will be the only significant change to the grass court season, with tournaments such as those at Queen's and Eastbourne unaffected.