The Welsh Rugby Union (WRU) confirmed Howley has returned to Wales six days before the team's opening World Cup match against Georgia in order to "assist with an investigation in relation to a potential breach of World Rugby regulation 6, specifically betting on rugby union".
A WRU statement said: "The decision was taken to act immediately in light of recent information passed to the WRU.
"No further details can be provided at this stage as this would prejudice the investigation. If required an independent panel will be appointed to hear the case.
