Hales, who was named in England's provisional 15-man World Cup squad just last week, has not played for Nottinghamshire this season after making himself unavailable for his county just seven days ago for "personal reasons", Cricbuzz reports.
However, The Guardian reported on Friday that Hales is serving a three-week ban handed down by the England and Wales Cricket Board for failing a drugs test for the second time.
The ECB have refused to release an official statement on the matter, with a spokesperson for the organisation saying: "We have a duty of confidentiality, therefore we are unable to provide any further comment".
All professional male cricketers under the ECB's jurisdiction, along with centrally contracted female players, are subject to hair follicle testing at the start and end of each season. The testing of hair follicles means banned substances can be detected up to three months after their consumption.
Players that fail a recreational drug test for the first time are not named, with the matter dealt with internally by the ECB and the Professional Cricketers's Association who in turn offer rehabilitative support. Once a test is failed for a second time, an automatic three-week ban comes into effect from the date the player is informed of the results, along with a fine of five per-cent of their annual salary. The player's county is informed, along with ECB chief executive Tom Harrison and PCA chief executive David Leatherdale. A third failed test and a player could have his domestic and international contract terminated immediately.
While the exact date of the notice handed to Hales is unknown, it is believed he will have served his 21-day ban before England's ODI against Ireland, their first international fixture of the summer, on May 3. And while the 30-year-old is in the preliminary World Cup squad, a rubber-stamped 15-man squad does not need to be confirmed to the ICC until May 23.
As such, Hales could find himself at the mercy of ECB's new director of men's cricket Ashley Giles, who is looking to take a tough stance against ill-discipline. In January of this year, Giles stated: "How we play and are viewed outwardly is important to [ECB chief executive] Tom Harrison and to [the chairman] Colin Graves but it is also really important to me. It's how we are seen and how we are respected."
Hales, for his part in the Bristol brawl in September 2017 that saw Ben Stokes arrested, received a ban of six limited overs matches (four suspended) and fined GBP 17,500 by the ECB. While he has returned to action and enjoyed success - though not in the best ODI XI, he is currently the first-reverse batsman - and remains a feared force in white ball cricket, with an international 50-over record of 2,419 runs at an average of 37.79 and six hundreds.
But, privately, he has been struggling since incident nearly two years ago and, with this indiscretion, may have seriously harmed his career in the short- and long-term. With Jason Roy and Joe Denly suffering back-spasms, Hales would have had a chance to push his case during the upcoming one-dayers against Ireland and Pakistan. He would also be in line to start a handful of England's nine World Cup group games.
He is still expected to meet up with the 15-man preliminary squad, plus Jofra Archer and Chris Jordan, in Cardiff on Saturday.
At present, the ECB, Nottinghamshire, the PCA and Hales' representatives have declined to comment.