LONDON (AFP) - Aston Villa's rising star Jack Grealish has been warned about his future conduct by manager Tim Sherwood after becoming the latest Premier League footballer to be pictured inhaling nitrous oxide or "laughing gas".

Pictures of Grealish, a key figure in Villa's 2-1 FA Cup semi-final win over Liverpool at Wembley last weekend, inhaling nitrous oxide from a balloon were published in the British national press on Thursday.

It has been reported the photographs were taken a year ago.

Although legal in Britain, nitrous oxide has potentially damaging side-effects and the now 19-year-old midfielder follows Liverpool forward Raheem Sterling and West Bromwich Albion striker Saido Berahino in being pictured taking "laughing gas".

"I'm not pleased obviously," Villa manager Sherwood said on Thursday. "I spoke to Jack first thing this morning as he came in, I explained to him his behaviour can't be tolerated by the football club, we can't condone that behaviour, but, as I said about Raheem last week, he's a young man, he was even younger a year earlier when the picture was taken."