Given extra time off after their South Africa exertions, Wayne Rooney, Patrice Evra, Michael Carrick, Nemanja Vidic and Ji-sung Park are all due to report for tests at Carrington this week.
The Reds' fitness coach Tony Strudwick revealed last week that the quintet would be put on "accelerated programmes" to get them as fit as possible for the start of the campaign.
And Evra, who last week attended the opening of Park’s new football academy in Seoul, knows a proper pre-season is vital if United are to hit the ground running.
The defender told ManUtd.kr: "Pre-season is really important, and especially so for the World Cup players who’ve missed the tour. We’ll be training very hard to get ready.
"I remember when I first arrived at United [in January 2006], I found it hard because I hadn’t had the same pre-season as the other players. It's the time when you improve your fitness, bond with your team-mates and work on tactics."
Building up match sharpness has been the priority in United’s friendlies so far, but Evra insists it’s also useful to get the right results along the way.
"Some might say friendlies are unimportant, but we always try to win because we then maintain that positive mentality when the real competitions start," he added.