Roberto Di Matteo confirmed on Thursday that an internal investigation has started at the club into media publicity surrounding Aston Villa’s Jack Grealish.

The manager refused to confirm newspaper suggestions that the midfielder is set to be fined two weeks’ wages following the player’s latest off-field indiscretions, which allegedly concern an all-night party at a Birmingham hotel on Saturday evening, or that the midfielder will be dropped but did reveal his disappointment following the latest publicity.

Di Matteo said: “[The investigation is] still ongoing, I cannot confirm or deny if he will be available. It’s a timing issue and we want to get it right. In general for the sake of any player they need to learn about what it takes to be an athlete. He needs to grow up very quickly.

“It’s not the first time and he needs to understand if he wants a good career he has to stop.”

He added: “First it’s a feeling of disappointment. I expect all players to behave in a professional manner at all times. We instantly started an investigation which is still ongoing. Once it’s finished and we have all the facts then we will take disciplinary action. This is the stance.”

On Wednesday the Aston Villa owner, Tony Xia, urged Grealish to show focus and avoid going in the “wrong direction” following the allegations, namely that he angered fellow guests at the hotel the club stayed at following Villa’s weekend goalless draw at Ipswich. The reports claimed fellow party-goers were inhaling nitrous oxide. There is no suggestion Grealish joined them in doing so.

Grealish’s off-field conduct has been the subject of adverse publicity before. In April 2015 he had to apologise to then Villa manager Tim Sherwood after being pictured inhaling from balloons at a party.

Photographs emerged last summer of the player lying on the ground, apparently drunk, while on holiday in Tenerife. The Villa academy product was then pictured on a night out just hours after a humiliating 4-0 defeat at Everton in November which led to the former manager Remi Garde banishing him to the under-21 side.

Grealish had made an encouraging start to the new campaign in the Championship following Villa’s relegation, scoring two goals in eight appearances and signing a new deal to keep him at the club until 2020.