It is the time of year where footballers are put through tough fitness regimes ahead of the new campaign.
However, despite the fact that there is some hard work ahead, Brazilian defender Rafael has insisted that he has always found the sessions "enjoyable".
"Pre-season is always good, it's enjoyable. I like this stage of the year a lot. Of course, there is a lot of running," he told the club's official website.
"But it's good as well because when you come back from holiday, sometimes you can get tired from doing nothing. I feel good when I'm working."
The United players start training tomorrow morning.