Alexis Sanchez and Mason Greenwood had very contrasting summers. 

The Chilean forward picked up a hamstring injury while playing at the Copa America and has been desperately trying to return to fitness ever since. 

Even when he does get back to full fitness, it's unclear if he'll be able to hold down a starting place at Old Trafford, given his dreadful Manchester United career to date. 

Sanchez's young teammate, on the other hand, looks ready to break into Ole Gunnar Solskjaer's team.

Greenwood seriously impressed during a number of friendlies and he'll be aiming to make a real impression this season. 

The two players couldn't be further apart in their careers right now, but in a recent training session, they collided in quite spectacular fashion. 

According to The Sun, Greenwood fouled Sanchez in one of his first sessions back in Manchester, leading to a furious 'bust-up'.

The report suggests that 'angry words' were exchanged between the pair and United's number seven was left 'fuming' after the incident. 

It's certainly not ideal preparation ahead of a season that's so important for the Red Devils.  

A separate report suggests that Sanchez has also been training away from the first-team squad in his bid to return as quickly as possible. 

But against Chelsea on Sunday, United proved that they probably won't miss him this season. 

They battered the Blues 4-0 thanks to a Marcus Rashford brace and goals from Anthony Martial and Daniel James. 

With Solskjaer apparently putting an emphasis on changing the culture at Old Trafford this year, Sanchez may find himself left behind. 

There have already been suggestions that AS Roma are pushing to take him on loan this season and if that does happen, then it would be no exaggeration to suggest that his United career would be over.