The International Tennis Federation (ITF) has confirmed an investigation has been opened over umpire Denis Pitner's apparent breach of a 12-month suspension.
Croatian official Pitner received a year-long ban from the ITF in August 2015 for betting offences.
However, the Guardian alleged last week that Pitner had nevertheless worked as a line judge at the 2015 US Open - quoting a United States Tennis Association spokesman who expressed shock at the oversight.
A statement on Monday from the governing body read: "The ITF was made aware last Friday, 12 February 2016, that Denis Pitner, an official from Croatia, previously suspended for one year by the ITF commencing 1 August 2015 under the Officiating Code of Conduct, had apparently breached terms of his suspension.
"The ITF immediately opened an investigation into these potential breaches and a notice of investigation has been issued to Mr. Pitner.
"Following this investigation, any additional sanction will be announced."
Tennis was rocked last month when allegations of widespread match-fixing were made ahead of the Australian Open, following a joint investigation by BuzzFeed and the BBC.
An independent review panel has since been set up to review the effectiveness of the Tennis Anti-Corruption Programme (TACP), the Tennis Integrity Unit (TIU) and the Tennis Integrity Protection Programme (TIPP) and recommend any changes.