Greenwood clearly lacks the maturity at his age of, say, Marcus Rashford. Hopefully this is just gossip, or if it is correct, can be dealt with and he moves on. There have been a number of separate incidents now, though, that ring alarm bells, in the sense that the incidents themselves are trivial but look as if they point to a problem of attitude.
There have certainly been players with controversial lifestyles - Rooney, for instance, and most certainly Cristiano Ronaldo. In their cases, they have been aired in the media, but the players managed to separate their approach to their private or social lives from their attitudes to their football. Nobody would question Ronaldo's commitment to his fitness or improving his football skills (although Rooney's lifestyle was criticised at times for the impact it was said to have on his fitness), and generally the controversies around them occurred well after they'd become established celebrities. They didn't have to contend with Twitter and the like during their earlier years.
Greenwood's behaviour (some of which we know about, some just media reports so far) fits more into the pattern of previous players who have shot to prominence at a young age and haven't had the maturity or intelligence to realise that they still need to put the work in and not let the sudden celebrity go to their heads. I remember Warren Joyce naming three who he said could have gone on to great things, but lacked the self-discipline to do the hard work once they came near the first team - Adnan Januzaj, James Wilson and Federico Macheda.
If this all sounds over-serious for a 19-year old misbehaving, the reality is that it could be the difference between being a world-class player (for which Greenwood clearly has the talent) and a shooting star who everyone remembers for what he could have been if he'd knuckled down. As Ole said the other day, it's what's between the ears that makes the difference.